Allow User to input HTML in ASP.NET MVC - ValidateInput or AllowHtml

Add to model:

using System.Web.Mvc;

And to your property

        [AllowHtml]
        [Display(Name = "Body")]
        public String Body { get; set; }

This code from my point the best way avoid this error. If you are using HTML editor you will not have security issues because it already restricted.

Add the following attribute the action (post) in the controller that you want to allow HTML for:

[ValidateInput(false)] 

Edit: As per Charlino comments:

In your web.config set the validation mode used. See MSDN:

<httpRuntime requestValidationMode="2.0" />

Edit Sept 2014: As per sprinter252 comments:

You should now use the [AllowHtml] attribute. See below from MSDN:

For ASP.NET MVC 3 applications, when you need to post HTML back to your model, don’t use ValidateInput(false) to turn off Request Validation. Simply add [AllowHtml] to your model property, like so:

public class BlogEntry {
    public int UserId {get;set;}
    [AllowHtml] 
    public string BlogText {get;set;}
 }

What about [AllowHtml] attribute above property?