Be warned that cookie names are case sensitive. <%@ Page Language="C#" %>"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> Set Cookie id="lblCookieValue" Text="Cookie Value:" AssociatedControlID="txtCookieValue" Runat="server" /> id="txtCookieValue" Runat="server" /> id="btnAdd" Text="Add Value" OnClick="btnAdd_Click" Runat="server" />