API: http://james.newtonking.com/projects/json/help/

Json.NET

The Json.NET library makes working with JavaScript and JSON formatted data in .NET simple. Quickly read and write JSON using the JsonReader and JsonWriter or serialize your .NET objects with a single method call using the JsonSerializer. 

• LINQ to JSON
• Lightning fast JsonReader and JsonWriter
• The JsonSerializer for quickly converting your .NET objects to JSON and back again
• Json.NET can optionally produce well formatted, indented JSON for debugging or display
• Attributes like JsonIgnore and JsonProperty can be added to a class to customize how a class is serialized
• Ability to convert JSON to and from XML

Example

Product product = new Product();

product.Name = "Apple";

product.Expiry = new DateTime(2008, 12, 28);

product.Price = 3.99M;

product.Sizes = new string[] { "Small", "Medium", "Large" };

string json = JavaScriptConvert.SerializeObject(product);

//{

//  "Name": "Apple",

//  "Expiry": new Date(1230422400000),

//  "Price": 3.99,

//  "Sizes": [

//    "Small",

//    "Medium",

//    "Large"

//  ]

/