In many cases, elements or controls on your page must refer to an external resource such as an image or another *.aspx file. To refer to these resources I prefer to use relative paths, because on my development machine the URL might be http//:localhost but on the production machine the URL might have a host header, like http://mywebapp.roelvanlisdonk.nl. or an other port like http://localhost:81.

When using relative paths there are two kinds of elements

• Not web server controls like (html tags, css statements etc.)
• Web server controls (ASP .NET server controls)

Not web server controls (html tags, css statements etc.)

Always start an URL with a "/", no matter where you are in the tree structure, this relative URL will always work

• "/Images/Logo.png"
• <img alt="Logo" src="/Images/Logo.png" />

Don’t use:

• "../" like "../Images/Logo.png"
• "no slash at all" like "Images/Logo.png"

Web server controls

Always start an URL with a "~/"

• "~/Images/Logo.png"
• Response.Redirect("~/Pages/MyPage.aspx");
• <asp:HyperLink ID="HyperLink1" runat="server" navigateUrl="~/Pages/Default.aspx">Test HyperLink</asp:HyperLink>

Don’t use:

• "/" like "/Images/Logo.png"
• "../" like "../Images/Logo.png"
• "no slash at all" like "Images/Logo.png"

See: http://msdn.microsoft.com/en-us/library/ms178116.aspx