 <p><code>&lt;%= myfunction(); %></code> would be used to output the return value of <code>myfunction</code> in a page.</p> <p><code>&lt;%# myfunction(); %></code> would be used to output the return value of <code>myfunction</code> in a control that is data bound (for example, inside an asp repeater control).</p> <p>Take a look at <a href="http://support.microsoft.com/kb/307860#1a" rel="nofollow noreferrer">this overview</a> for more information on data binding.</p>