diff --git a/csharp-es/Domain/Account.cs b/csharp-es/Domain/Account.cs
new file mode 100644
index 0000000..4a744d7
--- /dev/null
+++ b/csharp-es/Domain/Account.cs
@@ -0,0 +1,93 @@
+using CsharpEs.Library;
+
+namespace CsharpEs.Domain;
+
+public sealed record AccountState(Guid Id);
+
+public abstract record AccountCommand
+{
+    public sealed record OpenAccount(Guid AccountId, Money OpeningBalance) : AccountCommand;
+
+    public sealed record WithdrawMoney(Guid AccountId, Money Amount) : AccountCommand;
+
+    public sealed record DepositMoney(Guid AccountId, Money Amount) : AccountCommand;
+}
+
+public abstract record AccountEvent(Guid AccountId)
+{
+    public sealed record AccountOpened(Guid AccountId, Money OpeningBalance)
+        : AccountEvent(AccountId);
+
+    public sealed record MoneyWithdrawn(Guid AccountId, Money Amount) : AccountEvent(AccountId);
+
+    public sealed record MoneyDeposited(Guid AccountId, Money Amount) : AccountEvent(AccountId);
+}
+
+public abstract record AccountError
+{
+    public sealed record AccountNotFound : AccountError;
+
+    public sealed record AccountOpenAlready : AccountError;
+
+    public sealed record OpeningBalanceMustBeNonNegative : AccountError;
+
+    public sealed record InnerException(Exception exception) : AccountError;
+}
+
+public static class AccountDecider
+{
+    public static Result<AccountEvent, AccountError> Decide(
+        AccountState? state,
+        AccountCommand command
+    ) =>
+        Result<AccountEvent, AccountError>.Catch(
+            () =>
+                (state, command) switch
+                {
+                    // if this is a new account, check for valid opening balance
+                    (null, AccountCommand.OpenAccount c) when c.OpeningBalance.Amount < 0m =>
+                        Result<AccountEvent, AccountError>.Fail(
+                            new AccountError.OpeningBalanceMustBeNonNegative()
+                        ),
+
+                    // still a new account, now we can open it
+                    (null, AccountCommand.OpenAccount c) => Result<AccountEvent, AccountError>.Ok(
+                        new AccountEvent.AccountOpened(c.AccountId, c.OpeningBalance)
+                    ),
+
+                    // if we have an account already, you can't open it
+                    (not null, AccountCommand.OpenAccount c) => Result<
+                        AccountEvent,
+                        AccountError
+                    >.Fail(new AccountError.AccountOpenAlready()),
+
+                    (null, _) => Result<AccountEvent, AccountError>.Fail(
+                        new AccountError.AccountNotFound()
+                    ),
+
+                    (_, AccountCommand.WithdrawMoney c) => Result<AccountEvent, AccountError>.Ok(
+                        new AccountEvent.MoneyWithdrawn(c.AccountId, c.Amount)
+                    ),
+
+                    (_, AccountCommand.DepositMoney c) => Result<AccountEvent, AccountError>.Ok(
+                        new AccountEvent.MoneyDeposited(c.AccountId, c.Amount)
+                    ),
+
+                    _ => throw new InvalidOperationException("Unknown command."),
+                },
+            e => new AccountError.InnerException(e)
+        );
+
+    public static Result<AccountState?, AccountError> Evolve(
+        AccountState? state,
+        AccountEvent @event
+    ) =>
+        (state, @event) switch
+        {
+            (null, AccountEvent.AccountOpened e) => Result<AccountState?, AccountError>.Ok(
+                new AccountState(e.AccountId)
+            ),
+
+            _ => Result<AccountState?, AccountError>.Ok(state),
+        };
+}
diff --git a/csharp-es/Domain/Money.cs b/csharp-es/Domain/Money.cs
new file mode 100644
index 0000000..c776726
--- /dev/null
+++ b/csharp-es/Domain/Money.cs
@@ -0,0 +1,3 @@
+namespace CsharpEs.Domain;
+
+public sealed record Money(decimal Amount);
diff --git a/csharp-es/Infrastructure/AccountReadModel.cs b/csharp-es/Infrastructure/AccountReadModel.cs
new file mode 100644
index 0000000..e292d7f
--- /dev/null
+++ b/csharp-es/Infrastructure/AccountReadModel.cs
@@ -0,0 +1,108 @@
+using System.Collections.Immutable;
+using CsharpEs.Domain;
+using CsharpEs.Library;
+
+namespace CsharpEs.Infrastructure;
+
+public abstract record ReadModelError
+{
+    public sealed record AccountDetailsNotFound : ReadModelError;
+}
+
+public sealed record AccountBalanceReadModel(
+    Func<AccountEvent, Result<AccountDetails, ReadModelError>> Project,
+    Func<Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError>> Query
+);
+
+[Flags]
+public enum AccountFlags
+{
+    None = 0,
+    InOverdraft = 1,
+}
+
+public sealed record AccountDetails(Money Balance, AccountFlags Flags);
+
+public static class AccountBalanceReadModelModule
+{
+    public static Result<AccountBalanceReadModel, ReadModelError> Create()
+    {
+        // This is our read-model specific "persistent" storage
+        var modelData = ImmutableDictionary<Guid, AccountDetails>.Empty;
+
+        Result<AccountDetails, ReadModelError> Project(AccountEvent @event)
+        {
+            Logging.Output("rm", "Projecting event", @event);
+            switch (@event)
+            {
+                case AccountEvent.AccountOpened e:
+                    modelData = modelData.SetItem(
+                        e.AccountId,
+                        new AccountDetails(e.OpeningBalance, AccountFlags.None)
+                    );
+                    break;
+
+                case AccountEvent.MoneyWithdrawn e:
+                    {
+                        if (modelData.TryGetValue(e.AccountId, out var oldDetails))
+                        {
+                            var newBalance = new Money(oldDetails.Balance.Amount - e.Amount.Amount);
+                            modelData = modelData.SetItem(
+                                e.AccountId,
+                                oldDetails with
+                                {
+                                    Balance = newBalance,
+                                    Flags = CalcAccountFlags(newBalance, oldDetails),
+                                }
+                            );
+                        }
+                        else
+                            return Result<AccountDetails, ReadModelError>.Fail(
+                                new ReadModelError.AccountDetailsNotFound()
+                            );
+                    }
+                    break;
+
+                case AccountEvent.MoneyDeposited e:
+                    {
+                        if (modelData.TryGetValue(e.AccountId, out var oldDetails))
+                        {
+                            var newBalance = new Money(oldDetails.Balance.Amount + e.Amount.Amount);
+                            modelData = modelData.SetItem(
+                                e.AccountId,
+                                oldDetails with
+                                {
+                                    Balance = newBalance,
+                                    Flags = CalcAccountFlags(newBalance, oldDetails),
+                                }
+                            );
+                        }
+                        else
+                            return Result<AccountDetails, ReadModelError>.Fail(
+                                new ReadModelError.AccountDetailsNotFound()
+                            );
+                    }
+                    break;
+            }
+
+            // Read model-side "project" may not normally return any data, but for demo
+            // purposes we return the affected data directly to save us modeling a separate
+            // query side.
+            return Result<AccountDetails, ReadModelError>.Ok(modelData[@event.AccountId]);
+        }
+
+        Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError> Query() =>
+            Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError>.Ok(modelData.ToArray());
+
+        return Result<AccountBalanceReadModel, ReadModelError>.Ok(
+            new AccountBalanceReadModel(Project, Query)
+        );
+    }
+
+    private static AccountFlags CalcAccountFlags(Money newBalance, AccountDetails oldDetails)
+    {
+        return newBalance.Amount < 0
+            ? oldDetails.Flags | AccountFlags.InOverdraft
+            : oldDetails.Flags & ~AccountFlags.InOverdraft;
+    }
+}
diff --git a/csharp-es/Library/Logging.cs b/csharp-es/Library/Logging.cs
new file mode 100644
index 0000000..ce58f5f
--- /dev/null
+++ b/csharp-es/Library/Logging.cs
@@ -0,0 +1,59 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace CsharpEs.Library;
+
+public static class Logging
+{
+    public static T LogReturn<T>(string message, T r)
+    {
+        Console.WriteLine(message);
+        return r;
+    }
+
+    static string Indent(string text, int indent = 4)
+    {
+        var prefix = new string(' ', indent);
+
+        return Environment.NewLine
+            + string.Join(
+                Environment.NewLine,
+                text.Split(Environment.NewLine).Select(line => prefix + line)
+            );
+    }
+
+    public static string Format(Object? o) =>
+        o != null
+            ? Indent(
+                JsonSerializer.Serialize(
+                    o,
+                    new JsonSerializerOptions
+                    {
+                        WriteIndented = true,
+                        Converters = { new JsonStringEnumConverter() },
+                    }
+                )
+            )
+            : "(null)";
+
+    public static void Output(string src, string message, Object? x)
+    {
+        Console.WriteLine($"[{src}] {message} | {Format(x)}");
+    }
+
+    public static void Output(string src, string message)
+    {
+        Console.WriteLine($"[{src}] {message}");
+    }
+
+    public static Action<T> OutputDelegate<T>(string src, string message) =>
+        x =>
+        {
+            Output(src, message, x);
+        };
+
+    public static void OutputError<T>(string src, T error)
+    {
+        Console.Error.WriteLine($"\e[1;31m[{src} ERROR]\e[0m {Format(error)}");
+    }
+}
diff --git a/csharp-es/Library/Result.cs b/csharp-es/Library/Result.cs
new file mode 100644
index 0000000..57f55e7
--- /dev/null
+++ b/csharp-es/Library/Result.cs
@@ -0,0 +1,138 @@
+namespace CsharpEs.Library;
+
+public readonly record struct Result<T, E>
+{
+    private readonly T _value;
+
+    private readonly E _error;
+
+    public bool IsSuccess { get; }
+
+    public bool IsFailure => !IsSuccess;
+
+    public T Value =>
+        IsSuccess
+            ? _value
+            : throw new InvalidOperationException("No value present for failed result.");
+
+    public E Error =>
+        IsFailure
+            ? _error
+            : throw new InvalidOperationException("No error present for successful result.");
+
+    private Result(T value)
+    {
+        _value = value;
+        _error = default!;
+        IsSuccess = true;
+    }
+
+    private Result(E error)
+    {
+        _value = default!;
+        _error = error;
+        IsSuccess = false;
+    }
+
+    public static Result<T, E> Ok(T value) => new(value);
+
+    public static Result<T, E> Fail(E error) => new(error);
+
+    public TResult Match<TResult>(Func<T, TResult> onSuccess, Func<E, TResult> onFailure) =>
+        IsSuccess ? onSuccess(_value) : onFailure(_error);
+
+    public void Switch(Action<T> onSuccess, Action<E> onFailure)
+    {
+        if (IsSuccess)
+            onSuccess(_value);
+        else
+            onFailure(_error);
+    }
+
+    public static Result<T, E> Catch(Func<T> f, Func<Exception, E> exceptionMapper)
+    {
+        try
+        {
+            var result = f();
+            return Result<T, E>.Ok(result);
+        }
+        catch (Exception e)
+        {
+            return Result<T, E>.Fail(exceptionMapper(e));
+        }
+    }
+
+    public static Result<T, E> Catch(Func<Result<T, E>> f, Func<Exception, E> exceptionMapper)
+    {
+        try
+        {
+            return f();
+        }
+        catch (Exception e)
+        {
+            return Result<T, E>.Fail(exceptionMapper(e));
+        }
+    }
+}
+
+public static class ResultExtensions
+{
+    public static Result<TOut, E> Bind<TIn, TOut, E>(
+        this Result<TIn, E> result,
+        Func<TIn, Result<TOut, E>> binder
+    ) => result.IsSuccess ? binder(result.Value) : Result<TOut, E>.Fail(result.Error);
+
+    public static Result<TOut, E> Map<TIn, TOut, E>(
+        this Result<TIn, E> result,
+        Func<TIn, TOut> mapper
+    ) =>
+        result.IsSuccess
+            ? Result<TOut, E>.Ok(mapper(result.Value))
+            : Result<TOut, E>.Fail(result.Error);
+
+    public static Result<T, E> Tap<T, E>(this Result<T, E> result, Action<T> action)
+    {
+        if (result.IsSuccess)
+            action(result.Value);
+
+        return result;
+    }
+
+    public static Result<T, E> TapError<T, E>(this Result<T, E> result, Action<E> action)
+    {
+        if (result.IsFailure)
+            action(result.Error);
+
+        return result;
+    }
+
+    public static Result<T, EOut> MapError<T, EIn, EOut>(
+        this Result<T, EIn> result,
+        Func<EIn, EOut> map
+    ) =>
+        result.IsSuccess
+            ? Result<T, EOut>.Ok(result.Value)
+            : Result<T, EOut>.Fail(map(result.Error));
+
+    public static Result<T, E> Log<T, E>(this Result<T, E> result, string src, string msg) =>
+        Tap(result, Logging.OutputDelegate<T>(src, msg)).TapError(m => Logging.OutputError(src, m));
+
+    public static Result<T, E> Log<T, E>(
+        this Result<T, E> result,
+        string src,
+        Func<T, string> renderText
+    ) =>
+        Tap(result, x => Logging.OutputDelegate<T>(src, renderText(x))(x))
+            .TapError(m => Logging.OutputError(src, m));
+
+    public static Result<TOut, E> Select<TIn, TOut, E>(
+        this Result<TIn, E> result,
+        Func<TIn, TOut> mapper
+    ) => result.Map(mapper);
+
+    public static Result<TOut, E> SelectMany<TIn, TIntermediate, TOut, E>(
+        this Result<TIn, E> result,
+        Func<TIn, Result<TIntermediate, E>> binder,
+        Func<TIn, TIntermediate, TOut> projector
+    ) => result.Bind(x => binder(x).Map(y => projector(x, y)));
+}
diff --git a/csharp-es/Program.cs b/csharp-es/Program.cs
new file mode 100644
index 0000000..83132dd
--- /dev/null
+++ b/csharp-es/Program.cs
@@ -0,0 +1,84 @@
+using System.Collections.Immutable;
+using CsharpEs.Domain;
+using CsharpEs.Infrastructure;
+using CsharpEs.Library;
+
+public abstract record DemoError
+{
+    public sealed record Account(AccountError Error) : DemoError;
+
+    public sealed record ReadModel(ReadModelError Error) : DemoError;
+}
+
+public class Program
+{
+    private static Guid accountId;
+    private static ImmutableList<AccountCommand> demoCommands = ImmutableList<AccountCommand>.Empty;
+
+    static Program()
+    {
+        accountId = Guid.NewGuid();
+        demoCommands = demoCommands.AddRange([
+            new AccountCommand.OpenAccount(accountId, new Money(-200m)),
+            //            new AccountCommand.OpenAccount(accountId, new Money(200m)),
+            new AccountCommand.WithdrawMoney(accountId, new Money(100m)),
+            new AccountCommand.WithdrawMoney(accountId, new Money(200m)),
+            new AccountCommand.DepositMoney(accountId, new Money(500m)),
+        ]);
+    }
+
+    static ImmutableList<AccountEvent> eventStore = ImmutableList<AccountEvent>.Empty;
+
+    static Result<AccountState?, DemoError> ApplyEvent(
+        AccountBalanceReadModel balanceProjection,
+        AccountState? state,
+        AccountEvent @event
+    )
+    {
+        eventStore = eventStore.Add(@event);
+        Logging.Output(
+            "ae",
+            $"Applying event {Logging.Format(@event)} to state {Logging.Format(state)}"
+        );
+        return AccountDecider
+            .Evolve(state, @event)
+            .MapError(e => (DemoError)new DemoError.Account(e))
+            .Bind(newState =>
+                balanceProjection
+                    .Project(@event)
+                    .MapError(e => (DemoError)new DemoError.ReadModel(e))
+                    .Log("ae ad", "Account details")
+                    .Map(_ => newState)
+            )
+            .Log("ae", $"Applied and projected {Logging.Format(@event)}");
+    }
+
+    public static void Main(string[] args)
+    {
+        Logging.Output("csharp-es", "Starting money handling demo...");
+
+        AccountBalanceReadModelModule
+            .Create()
+            .MapError(e => (DemoError)new DemoError.ReadModel(e))
+            .Bind(readModel =>
+                demoCommands
+                    .Aggregate(
+                        Result<AccountState?, DemoError>.Ok(null),
+                        (stateResult, command) =>
+                            stateResult.Bind(state =>
+                                AccountDecider
+                                    .Decide(state, command)
+                                    .MapError(e => (DemoError)new DemoError.Account(e))
+                                    .Bind(@event => ApplyEvent(readModel, state, @event))
+                            )
+                    )
+                    .Bind(s =>
+                        readModel
+                            .Query()
+                            .Log("query", "Read model data")
+                            .MapError(e => (DemoError)new DemoError.ReadModel(e))
+                    )
+            )
+            .Log("csharp-es done", "Demo completed.");
+    }
+}
diff --git a/csharp-es/csharp-es.csproj b/csharp-es/csharp-es.csproj
new file mode 100644
index 0000000..a955afb
--- /dev/null
+++ b/csharp-es/csharp-es.csproj
@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <RootNamespace>CsharpEs</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+</Project>
diff --git a/csharp.sln b/csharp.sln
index c9767a6..7bc0312 100644
--- a/csharp.sln
+++ b/csharp.sln
@@ -25,6 +25,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-fp3", "csharp-fp3\cs
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-fp3.Tests", "csharp-fp3.Tests\csharp-fp3.Tests.csproj", "{B85327F8-AFA8-47E9-97AB-318F74238929}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-es", "csharp-es\csharp-es.csproj", "{748A2E36-A131-4EAA-A403-E54E347010C0}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -143,6 +145,18 @@ Global
 		{B85327F8-AFA8-47E9-97AB-318F74238929}.Release|x64.Build.0 = Release|Any CPU
 		{B85327F8-AFA8-47E9-97AB-318F74238929}.Release|x86.ActiveCfg = Release|Any CPU
 		{B85327F8-AFA8-47E9-97AB-318F74238929}.Release|x86.Build.0 = Release|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Debug|x64.Build.0 = Debug|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Debug|x86.Build.0 = Debug|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Release|Any CPU.Build.0 = Release|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Release|x64.ActiveCfg = Release|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Release|x64.Build.0 = Release|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Release|x86.ActiveCfg = Release|Any CPU
+		{748A2E36-A131-4EAA-A403-E54E347010C0}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -157,5 +171,6 @@ Global
 		{4AFF063B-7125-4783-BE84-E1E9B4E2A462} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
 		{83AFEF87-AAC9-45F4-B803-1BCDF0443BF7} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
 		{B85327F8-AFA8-47E9-97AB-318F74238929} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
+		{748A2E36-A131-4EAA-A403-E54E347010C0} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
 	EndGlobalSection
 EndGlobal