diff --git a/EnvelopeGenerator.DependencyInjection/DependencyInjection.cs b/EnvelopeGenerator.DependencyInjection/DependencyInjection.cs
new file mode 100644
index 00000000..cebe6df9
--- /dev/null
+++ b/EnvelopeGenerator.DependencyInjection/DependencyInjection.cs
@@ -0,0 +1,108 @@
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using EnvelopeGenerator.Application;
+using EnvelopeGenerator.Application.Common.Interfaces.Services;
+using EnvelopeGenerator.Application.Services;
+using EnvelopeGenerator.Infrastructure;
+
+namespace EnvelopeGenerator.DependencyInjection;
+
+/// <summary>
+/// Extension methods for registering EnvelopeGenerator services into an <see cref="IServiceCollection"/>.
+/// Use <see cref="AddEnvelopeGenerator"/> as the single entry-point for projects that need both the
+/// application layer (MediatR, AutoMapper, CRUD services, configuration sections) and the infrastructure
+/// layer (repositories, DbContext, SQL executors).
+/// For projects that do not need a database (e.g. lightweight API gateways or unit-test hosts), use
+/// <see cref="AddEnvelopeGeneratorCore"/> to register only the application layer.
+/// </summary>
+public static class DependencyInjection
+{
+    /// <summary>
+    /// Registers the full EnvelopeGenerator stack – application <em>and</em> infrastructure services – into
+    /// the provided <see cref="IServiceCollection"/>.
+    /// <para>
+    /// Internally this calls <c>AddEnvelopeGeneratorServices</c> (application layer) and
+    /// <c>AddEnvelopeGeneratorInfrastructureServices</c> (infrastructure layer).
+    /// A <see cref="Microsoft.EntityFrameworkCore.DbContext"/> and / or <c>DbTriggerParams</c> must be
+    /// configured through <paramref name="infrastructureOptions"/>; without it no database connection will
+    /// be established at runtime.
+    /// </para>
+    /// </summary>
+    /// <param name="services">Service collection to register services into.</param>
+    /// <param name="configuration">
+    ///     Application configuration. Used to bind <c>DispatcherParams</c>, <c>MailParams</c>,
+    ///     <c>AuthenticatorParams</c>, <c>TotpSmsParams</c>, <c>GtxMessagingParams</c> and other
+    ///     application-level option sections.
+    /// </param>
+    /// <param name="infrastructureOptions">
+    ///     Optional callback to configure the infrastructure layer registration.
+    ///     Typical usage:
+    ///     <code>
+    ///     services.AddEnvelopeGenerator(config, opt =>
+    ///     {
+    ///         opt.AddDbContext(o => o.UseSqlServer(connectionString));
+    ///         opt.AddDbTriggerParams(config);
+    ///     });
+    ///     </code>
+    /// </param>
+    /// <returns>The updated <see cref="IServiceCollection"/>.</returns>
+#pragma warning disable CS0618 // AddEnvelopeGeneratorServices / AddEnvelopeGeneratorInfrastructureServices are intentionally wrapped here
+    public static IServiceCollection AddEnvelopeGenerator(
+        this IServiceCollection services,
+        IConfiguration configuration,
+        Action<EnvelopeGenerator.Infrastructure.DependencyInjection.Config>? infrastructureOptions = null)
+    {
+        // Application layer: CRUD services, MediatR, AutoMapper, configuration sections.
+        services.AddEnvelopeGeneratorServices(configuration);
+
+        // Infrastructure layer: repositories, DbContext, Dapper type maps, SQL executors.
+        services.AddEnvelopeGeneratorInfrastructureServices(opt =>
+        {
+            infrastructureOptions?.Invoke(opt);
+        });
+
+        return services;
+    }
+#pragma warning restore CS0618
+
+    /// <summary>
+    /// Registers only the <em>application</em> layer services (MediatR handlers, AutoMapper profiles,
+    /// CRUD services, configuration sections) without any infrastructure / database dependencies.
+    /// <para>
+    /// Useful for projects that already manage their own DbContext or do not require direct database
+    /// access, such as lightweight API gateways, console tools or unit/integration test hosts that
+    /// use an in-memory database configured elsewhere.
+    /// </para>
+    /// </summary>
+    /// <param name="services">Service collection to register services into.</param>
+    /// <param name="configuration">Application configuration used to bind application-level option sections.</param>
+    /// <returns>The updated <see cref="IServiceCollection"/>.</returns>
+#pragma warning disable CS0618
+    public static IServiceCollection AddEnvelopeGeneratorCore(
+        this IServiceCollection services,
+        IConfiguration configuration)
+    {
+        services.AddEnvelopeGeneratorServices(configuration);
+        return services;
+    }
+#pragma warning restore CS0618
+
+    /// <summary>
+    /// Registers <see cref="EnvelopeMailService"/> as the <see cref="IEnvelopeMailService"/> scoped
+    /// implementation.
+    /// <para>
+    /// Call this in addition to <see cref="AddEnvelopeGenerator"/> when the consuming project needs to
+    /// send envelope e-mails directly (e.g. a Worker Service or the Web project). Projects that rely
+    /// purely on MediatR commands to trigger mail delivery do not need to call this.
+    /// </para>
+    /// </summary>
+    /// <param name="services">Service collection to register services into.</param>
+    /// <returns>The updated <see cref="IServiceCollection"/>.</returns>
+#pragma warning disable CS0618
+    public static IServiceCollection AddEnvelopeMailService(this IServiceCollection services)
+    {
+        services.AddScoped<IEnvelopeMailService, EnvelopeMailService>();
+        return services;
+    }
+#pragma warning restore CS0618
+}