diff --git a/src/CloudNative.CloudEvents/CloudEventFormatters.cs b/src/CloudNative.CloudEvents/CloudEventFormatters.cs
new file mode 100644
index 0000000..c13e230
--- /dev/null
+++ b/src/CloudNative.CloudEvents/CloudEventFormatters.cs
@@ -0,0 +1,205 @@
+// Copyright 2025 Cloud Native Foundation.
+// Licensed under the Apache 2.0 license.
+// See LICENSE file in the project root for full license information.
+
+using CloudNative.CloudEvents.Core;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net.Mime;
+using System.Threading.Tasks;
+
+namespace CloudNative.CloudEvents;
+
+/// <summary>
+/// Extension methods for <see cref="CloudEventFormatter"/>.
+/// </summary>
+public static class CloudEventFormatters
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="formatter"></param>
+    /// <param name="extensionAttributes"></param>
+    /// <returns></returns>
+    public static CloudEventFormatter WithDefaultDecodingExtensions(this CloudEventFormatter formatter, IEnumerable<CloudEventAttribute> extensionAttributes) =>
+        new DefaultExtensionsFormatter(formatter, extensionAttributes);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="formatter"></param>
+    /// <param name="validationAction"></param>
+    /// <returns></returns>
+    public static CloudEventFormatter WithValidation(this CloudEventFormatter formatter, Action<CloudEvent> validationAction) =>
+        WithValidation(formatter, validationAction, validationAction);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="formatter"></param>
+    /// <param name="encodingValidationAction"></param>
+    /// <param name="decodingValidationAction"></param>
+    /// <returns></returns>
+    public static CloudEventFormatter WithValidation(this CloudEventFormatter formatter, Action<CloudEvent>? encodingValidationAction, Action<CloudEvent>? decodingValidationAction) =>
+        new ValidatingFormatter(formatter, encodingValidationAction, decodingValidationAction);
+
+    /// <summary>
+    /// Delegating formatter which applies additional validation before each encoding method, and/or after each decoding method.
+    /// </summary>
+    private class ValidatingFormatter : DelegatingFormatter
+    {
+        private readonly Action<CloudEvent>? encodingValidationAction;
+        private readonly Action<CloudEvent>? decodingValidationAction;
+
+        internal ValidatingFormatter(CloudEventFormatter formatter, Action<CloudEvent>? encodingValidationAction, Action<CloudEvent>? decodingValidationAction) : base(formatter)
+        {
+            this.encodingValidationAction = encodingValidationAction;
+            this.decodingValidationAction = decodingValidationAction;
+        }
+
+        public override IReadOnlyList<CloudEvent> DecodeBatchModeMessage(ReadOnlyMemory<byte> body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes)
+        {
+            var result = base.DecodeBatchModeMessage(body, contentType, extensionAttributes);
+            foreach (var evt in result)
+            {
+                decodingValidationAction?.Invoke(evt);
+            }
+            return result;
+        }
+
+        public override IReadOnlyList<CloudEvent> DecodeBatchModeMessage(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes)
+        {
+            var result = base.DecodeBatchModeMessage(body, contentType, extensionAttributes);
+            foreach (var evt in result)
+            {
+                decodingValidationAction?.Invoke(evt);
+            }
+            return result;
+        }
+
+        public override async Task<IReadOnlyList<CloudEvent>> DecodeBatchModeMessageAsync(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes)
+        {
+            var result = await base.DecodeBatchModeMessageAsync(body, contentType, extensionAttributes).ConfigureAwait(false);
+            foreach (var evt in result)
+            {
+                decodingValidationAction?.Invoke(evt);
+            }
+            return result;
+        }
+
+        public override void DecodeBinaryModeEventData(ReadOnlyMemory<byte> body, CloudEvent cloudEvent)
+        {
+            base.DecodeBinaryModeEventData(body, cloudEvent);
+            decodingValidationAction?.Invoke(cloudEvent);
+        }
+
+        public override CloudEvent DecodeStructuredModeMessage(ReadOnlyMemory<byte> body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes)
+        {
+            var evt = base.DecodeStructuredModeMessage(body, contentType, extensionAttributes);
+            decodingValidationAction?.Invoke(evt);
+            return evt;
+        }
+
+        public override CloudEvent DecodeStructuredModeMessage(Stream messageBody, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes)
+        {
+            var evt = base.DecodeStructuredModeMessage(messageBody, contentType, extensionAttributes);
+            decodingValidationAction?.Invoke(evt);
+            return evt;
+        }
+
+        public override async Task<CloudEvent> DecodeStructuredModeMessageAsync(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes)
+        {
+            var evt = await base.DecodeStructuredModeMessageAsync(body, contentType, extensionAttributes).ConfigureAwait(false);
+            decodingValidationAction?.Invoke(evt);
+            return evt;
+        }
+
+        public override ReadOnlyMemory<byte> EncodeBatchModeMessage(IEnumerable<CloudEvent> cloudEvents, out ContentType contentType)
+        {
+            // This approach ensures that we only evaluate the original sequence once, without having to materialize it.
+            // It does mean we could end up encoding some before aborting later (and therefore wasting effort) though.
+            var validating = cloudEvents.Select(evt => { encodingValidationAction?.Invoke(evt); return evt; });
+            return base.EncodeBatchModeMessage(validating, out contentType);
+        }
+
+        public override ReadOnlyMemory<byte> EncodeBinaryModeEventData(CloudEvent cloudEvent)
+        {
+            encodingValidationAction?.Invoke(cloudEvent);
+            return base.EncodeBinaryModeEventData(cloudEvent);
+        }
+
+        public override ReadOnlyMemory<byte> EncodeStructuredModeMessage(CloudEvent cloudEvent, out ContentType contentType)
+        {
+            encodingValidationAction?.Invoke(cloudEvent);
+            return base.EncodeStructuredModeMessage(cloudEvent, out contentType);
+        }
+    }
+
+    /// <summary>
+    /// Delegating formatter which applies default extension attributes on all decoding method calls.
+    /// </summary>
+    private class DefaultExtensionsFormatter : DelegatingFormatter
+    {
+        private readonly IReadOnlyList<CloudEventAttribute> defaultExtensionAttributes;
+
+        internal DefaultExtensionsFormatter(CloudEventFormatter formatter, IEnumerable<CloudEventAttribute> extensionAttributes) : base(formatter)
+        {
+            defaultExtensionAttributes = Validation.CheckNotNull(extensionAttributes, nameof(extensionAttributes)).ToList().AsReadOnly();
+            foreach (var attribute in defaultExtensionAttributes)
+            {
+                if (!attribute.IsExtension)
+                {
+                    throw new ArgumentException($"The {nameof(CloudEventAttribute.IsExtension)} must be true for all default extension attributes", nameof(extensionAttributes));
+                }
+            }
+        }
+
+        public override IReadOnlyList<CloudEvent> DecodeBatchModeMessage(ReadOnlyMemory<byte> body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+            base.DecodeBatchModeMessage(body, contentType, ComputeEffectiveExtensionAttributes(extensionAttributes));
+
+        public override IReadOnlyList<CloudEvent> DecodeBatchModeMessage(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+            base.DecodeBatchModeMessage(body, contentType, ComputeEffectiveExtensionAttributes(extensionAttributes));
+
+        public override Task<IReadOnlyList<CloudEvent>> DecodeBatchModeMessageAsync(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+            base.DecodeBatchModeMessageAsync(body, contentType, ComputeEffectiveExtensionAttributes(extensionAttributes));
+
+        public override CloudEvent DecodeStructuredModeMessage(ReadOnlyMemory<byte> body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+            base.DecodeStructuredModeMessage(body, contentType, ComputeEffectiveExtensionAttributes(extensionAttributes));
+
+        public override CloudEvent DecodeStructuredModeMessage(Stream messageBody, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+            base.DecodeStructuredModeMessage(messageBody, contentType, ComputeEffectiveExtensionAttributes(extensionAttributes));
+
+        public override Task<CloudEvent> DecodeStructuredModeMessageAsync(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+            base.DecodeStructuredModeMessageAsync(body, contentType, ComputeEffectiveExtensionAttributes(extensionAttributes));
+
+        private IEnumerable<CloudEventAttribute> ComputeEffectiveExtensionAttributes(IEnumerable<CloudEventAttribute>? additionalExtensions)
+        {
+            if (additionalExtensions is null)
+            {
+                return defaultExtensionAttributes;
+            }
+            var result = new List<CloudEventAttribute>();
+
+            foreach (var additional in additionalExtensions)
+            {
+                var match = defaultExtensionAttributes.FirstOrDefault(def => def.Name == additional.Name);
+                if (match is not null)
+                {
+                    if (match != additional)
+                    {
+                        // TODO: Improve this message
+                        throw new ArgumentException($"The extension attribute {match.Name} is already provided as a default, using a different object");
+                    }
+                }
+                else
+                {
+                    result.Add(additional);
+                }
+            }
+            result.AddRange(defaultExtensionAttributes);
+            return result;
+        }
+    }
+}
diff --git a/src/CloudNative.CloudEvents/DelegatingFormatter.cs b/src/CloudNative.CloudEvents/DelegatingFormatter.cs
new file mode 100644
index 0000000..c444a14
--- /dev/null
+++ b/src/CloudNative.CloudEvents/DelegatingFormatter.cs
@@ -0,0 +1,151 @@
+// Copyright 2025 Cloud Native Foundation.
+// Licensed under the Apache 2.0 license.
+// See LICENSE file in the project root for full license information.
+
+using CloudNative.CloudEvents.Core;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Net.Mime;
+using System.Threading.Tasks;
+
+namespace CloudNative.CloudEvents;
+
+// TODO:
+// - Naming:
+//   - Is the namespace appropriate? We have very few types in this root namespace
+//   - Delegating or Decorating?
+//   - Fill in the "CloudEvent" part, e.g. DelegatingCloudEventFormatter?
+// - Expose the original formatter, perhaps in a protected way?
+// - All documentation
+// - We can't call original.InferContentType, because it's protected. Is that an issue? (Users can always override GetOrInferContentType instead.)
+// - Are we happy with this being public? With the extension methods being public, this class doesn't have to be.
+//   - Are we happy with the extension methods being extension methods?
+
+/// <summary>
+/// 
+/// </summary>
+public abstract class DelegatingFormatter : CloudEventFormatter
+{
+    /// <summary>
+    /// The formatter to delegate to.
+    /// </summary>
+    private readonly CloudEventFormatter original;
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="original"></param>
+    public DelegatingFormatter(CloudEventFormatter original)
+    {
+        this.original = Validation.CheckNotNull(original, nameof(original));
+    }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="body"></param>
+    /// <param name="contentType"></param>
+    /// <param name="extensionAttributes"></param>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    public override CloudEvent DecodeStructuredModeMessage(ReadOnlyMemory<byte> body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+        original.DecodeStructuredModeMessage(body, contentType, extensionAttributes);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="messageBody"></param>
+    /// <param name="contentType"></param>
+    /// <param name="extensionAttributes"></param>
+    /// <returns></returns>
+    public override CloudEvent DecodeStructuredModeMessage(Stream messageBody, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+        original.DecodeStructuredModeMessage(messageBody, contentType, extensionAttributes);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="body"></param>
+    /// <param name="contentType"></param>
+    /// <param name="extensionAttributes"></param>
+    /// <returns></returns>
+    public override Task<CloudEvent> DecodeStructuredModeMessageAsync(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+        original.DecodeStructuredModeMessageAsync(body, contentType, extensionAttributes);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="cloudEvent"></param>
+    /// <param name="contentType"></param>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    public override ReadOnlyMemory<byte> EncodeStructuredModeMessage(CloudEvent cloudEvent, out ContentType contentType) =>
+        original.EncodeStructuredModeMessage(cloudEvent, out contentType);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="body"></param>
+    /// <param name="cloudEvent"></param>
+    /// <exception cref="NotImplementedException"></exception>
+    public override void DecodeBinaryModeEventData(ReadOnlyMemory<byte> body, CloudEvent cloudEvent) =>
+        original.DecodeBinaryModeEventData(body, cloudEvent);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="cloudEvent"></param>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    public override ReadOnlyMemory<byte> EncodeBinaryModeEventData(CloudEvent cloudEvent) =>
+        original.EncodeBinaryModeEventData(cloudEvent);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="body"></param>
+    /// <param name="contentType"></param>
+    /// <param name="extensionAttributes"></param>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    public override IReadOnlyList<CloudEvent> DecodeBatchModeMessage(ReadOnlyMemory<byte> body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+        original.DecodeBatchModeMessage(body, contentType, extensionAttributes);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="body"></param>
+    /// <param name="contentType"></param>
+    /// <param name="extensionAttributes"></param>
+    /// <returns></returns>
+    public override IReadOnlyList<CloudEvent> DecodeBatchModeMessage(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+        original.DecodeBatchModeMessage(body, contentType, extensionAttributes);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="body"></param>
+    /// <param name="contentType"></param>
+    /// <param name="extensionAttributes"></param>
+    /// <returns></returns>
+    public override Task<IReadOnlyList<CloudEvent>> DecodeBatchModeMessageAsync(Stream body, ContentType? contentType, IEnumerable<CloudEventAttribute>? extensionAttributes) =>
+        original.DecodeBatchModeMessageAsync(body, contentType, extensionAttributes);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="cloudEvents"></param>
+    /// <param name="contentType"></param>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    public override ReadOnlyMemory<byte> EncodeBatchModeMessage(IEnumerable<CloudEvent> cloudEvents, out ContentType contentType) =>
+        original.EncodeBatchModeMessage(cloudEvents, out contentType);
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="cloudEvent"></param>
+    /// <returns></returns>
+    public override string? GetOrInferDataContentType(CloudEvent cloudEvent) =>
+        original.GetOrInferDataContentType(cloudEvent);
+}