HTTP/3 is the latest version of the Hypertext Transfer Protocol (HTTP) and it offers several improvements over its predecessors, including better performance, security, and scalability. In this article, we will explore how to use HTTP/3 in ASP.NET Core.   First, let's understand what HTTP/3 is and why it's important. HTTP/3 is a protocol that allows for faster and more efficient communication between web servers and clients. It uses the QUIC (Quick User Datagram Transport Interface) protocol as its underlying transport mechanism, which provides better performance and security compared to the previous versions of HTTP.   To use HTTP/3 in ASP.NET Core, you need to follow these steps:   1. Install the Microsoft.AspNetCore.HttpWebUtilities NuGet package. This package provides the necessary classes and methods for working with HTTP/3 in ASP.NET Core. 2. Create a new controller or action that will handle HTTP/3 requests. You can do this by adding the following code to your controller or action: csharp [HttpGet("{id}")] public IActionResult Get(int id) { // Your logic here } Note that you need to add the `HttpGet` attribute to specify that this is an HTTP GET request. 3. In your action, you can use the `HttpWebUtilities` class to create an instance of the `HttpClient` class and configure it to use HTTP/3. Here's an example: csharp public IActionResult Get(int id) { var client = new HttpClient(); client.DefaultRequestHeaders.Accept.Clear(); client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")); client.DefaultRequestHeaders.ConnectionClose = true; client.DefaultRequestHeaders.Upgrade = "h3"; var response = await client.GetAsync($"https://example.com/api/items/{id}"); // Your logic here } In this example, we're creating a new `HttpClient` instance and configuring it to use HTTP/3 by setting the `Upgrade` header to "h3". We're also setting the `ConnectionClose` header to true, which tells the server that the client is done sending requests and wants to close the connection. 4. Once you have configured your action to use HTTP/3, you can test it by making a request to your API endpoint using an HTTP/3-enabled browser or tool like Postman.   That's it! You have successfully used HTTP/3 in ASP.NET Core. Keep in mind that not all servers support HTTP/3 yet, so you may need to fall back to HTTP/2 or HTTP/1.1 if necessary. Additionally, you should always test your API thoroughly to ensure that it works as expected.