How can I add an ampersand for a value in a ASP.net/C# app config file value

Question

Use "&" instead of "&".

Have you tried this?

<appSettings>  
  <add key="myurl" value="http://www.myurl.com?&amp;cid=&amp;sid="/>
<appSettings>

I think you should be able to use the HTML escape character (&). They can be found at http://www.theukwebdesigncompany.com/articles/entity-escape-characters.php

Although the accepted answer here is technically correct, there seems to be some confusion amongst users based on the comments. When working with a ViewBag in a .cshtml file, you must use @Html.Raw otherwise your data, after being unescaped by the ConfigurationManager, will become re-escaped once again. Use Html.Raw() to prevent this from occurring.