diff --git a/EnvelopeGenerator.Application/Common/Behaviors/ValidationBehavior.cs b/EnvelopeGenerator.Application/Common/Behaviors/ValidationBehavior.cs
new file mode 100644
index 00000000..8752d045
--- /dev/null
+++ b/EnvelopeGenerator.Application/Common/Behaviors/ValidationBehavior.cs
@@ -0,0 +1,40 @@
+using DigitalData.Core.Exceptions;
+using FluentValidation;
+using MediatR;
+
+namespace EnvelopeGenerator.Application.Common.Behaviors;
+
+public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : notnull
+{
+    private readonly IEnumerable<IValidator<TRequest>> _validators;
+
+    public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
+    {
+        _validators = validators;
+    }
+
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+    {
+        if (_validators.Any())
+        {
+            var context = new ValidationContext<TRequest>(request);
+            var failures = _validators
+                .Select(v => v.Validate(context))
+                .SelectMany(r => r.Errors)
+                .Where(f => f is not null)
+                .ToList();
+
+            if (failures.Count > 0)
+            {
+                var message = string.Join("; ", failures.Select(f => f.ErrorMessage).Distinct());
+                throw new BadRequestException(message);
+            }
+        }
+
+        return await next();
+    }
+}
diff --git a/EnvelopeGenerator.Application/DependencyInjection.cs b/EnvelopeGenerator.Application/DependencyInjection.cs
index bf41d504..97c9757c 100644
--- a/EnvelopeGenerator.Application/DependencyInjection.cs
+++ b/EnvelopeGenerator.Application/DependencyInjection.cs
@@ -10,6 +10,8 @@ using System.Reflection;
 using MediatR;
 using EnvelopeGenerator.Application.DocReceiverElements.Commands;
 using EnvelopeGenerator.Application.DocReceiverElements.Behaviors;
+using EnvelopeGenerator.Application.Common.Behaviors;
+using FluentValidation;
 
 namespace EnvelopeGenerator.Application;
 
@@ -59,6 +61,9 @@ public static class DependencyInjection
         services.AddMediatR(cfg =>
         {
             cfg.RegisterServicesFromAssembly(Assembly.GetExecutingAssembly());
+
+            // Generic request validation
+            cfg.AddOpenBehavior(typeof(ValidationBehavior<,>));
             
             // Register SignCommand pipeline behaviors in execution order
             // 0. EnvelopeReceiverResolutionBehavior - Resolves EnvelopeReceiver from query parameters (executes FIRST)
@@ -80,6 +85,8 @@ public static class DependencyInjection
             cfg.AddBehavior<IPipelineBehavior<SigningCommand, Unit>, SendSignedMailBehavior>();
         });
 
+        services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly());
+
         return services;
     }
 }
diff --git a/EnvelopeGenerator.Application/Documents/Queries/ReadDocumentDetailsQueryValidator.cs b/EnvelopeGenerator.Application/Documents/Queries/ReadDocumentDetailsQueryValidator.cs
new file mode 100644
index 00000000..b9c88872
--- /dev/null
+++ b/EnvelopeGenerator.Application/Documents/Queries/ReadDocumentDetailsQueryValidator.cs
@@ -0,0 +1,13 @@
+using FluentValidation;
+
+namespace EnvelopeGenerator.Application.Documents.Queries;
+
+public class ReadDocumentDetailsQueryValidator : AbstractValidator<ReadDocumentDetailsQuery>
+{
+    public ReadDocumentDetailsQueryValidator()
+    {
+        RuleFor(x => x.EnvelopeId)
+            .GreaterThan(0)
+            .WithMessage("EnvelopeId is required.");
+    }
+}
diff --git a/EnvelopeGenerator.Application/Documents/Queries/ReadDocumentQueryValidator.cs b/EnvelopeGenerator.Application/Documents/Queries/ReadDocumentQueryValidator.cs
new file mode 100644
index 00000000..251d49eb
--- /dev/null
+++ b/EnvelopeGenerator.Application/Documents/Queries/ReadDocumentQueryValidator.cs
@@ -0,0 +1,23 @@
+using FluentValidation;
+
+namespace EnvelopeGenerator.Application.Documents.Queries;
+
+public class ReadDocumentQueryValidator : AbstractValidator<ReadDocumentQuery>
+{
+    public ReadDocumentQueryValidator()
+    {
+        RuleFor(x => x)
+            .Must(x => (x.Id ?? 0) > 0 || (x.EnvelopeId ?? 0) > 0)
+            .WithMessage("Id or EnvelopeId is required.");
+
+        RuleFor(x => x.Id)
+            .GreaterThan(0)
+            .When(x => x.Id.HasValue)
+            .WithMessage("Id must be greater than 0.");
+
+        RuleFor(x => x.EnvelopeId)
+            .GreaterThan(0)
+            .When(x => x.EnvelopeId.HasValue)
+            .WithMessage("EnvelopeId must be greater than 0.");
+    }
+}
diff --git a/EnvelopeGenerator.Application/EnvelopeGenerator.Application.csproj b/EnvelopeGenerator.Application/EnvelopeGenerator.Application.csproj
index 5ea118b7..b1b676c5 100644
--- a/EnvelopeGenerator.Application/EnvelopeGenerator.Application.csproj
+++ b/EnvelopeGenerator.Application/EnvelopeGenerator.Application.csproj
@@ -19,6 +19,8 @@
 		<PackageReference Include="DigitalData.Core.Client" Version="2.1.0" />
 		<PackageReference Include="DigitalData.Core.Exceptions" Version="1.1.0" />
 		<PackageReference Include="DigitalData.EmailProfilerDispatcher" Version="3.1.1" />
+		<PackageReference Include="FluentValidation" Version="11.11.0" />
+		<PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="11.11.0" />
 		<PackageReference Include="HtmlSanitizer" Version="9.0.892" />
 		<PackageReference Include="MediatR" Version="12.5.0" />
 		<PackageReference Include="Microsoft.Identity.Client" Version="4.82.1" />