Be warned that cookie names are case sensitive. <%@ Page Language="C#" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script runat="server"> protected void btnAdd_Click(object sender, EventArgs e) { Response.Cookies["message"].Value = txtCookieValue.Text; } </script> <html xmlns="http://www.w3.org/1999/xhtml" > <head id="Head1" runat="server"> <title>Set Cookie</title> </head> <body> <form id="form1" runat="server"> <div> <asp:Label id="lblCookieValue" Text="Cookie Value:" AssociatedControlID="txtCookieValue" Runat="server" /> <asp:TextBox id="txtCookieValue" Runat="server" /> <asp:Button id="btnAdd" Text="Add Value" OnClick="btnAdd_Click" Runat="server" /> </div> </form> </body> </html>