ASP.NET AJAX, formerly called Atlas, is a set of extensions to ASP.NET developed by Microsoft for implementing Ajax functionality. It is released under the Microsoft Public License (Ms-PL).
<asp:ButtonID="Button1"runat="server"Text="Refresh"/>
<asp:UpdatePanelID="UpdatePanel1"runat="server">
<Triggers>
<asp:AsyncPostBackTriggerControlID="Button1"EventName="Click"/>
</Triggers>
<ContentTemplate>
<span><%=DateTime.Now%>
</span>
</ContentTemplate>
</asp:UpdatePanel>
Web-services and JSON
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ASP.NET AJAX framework brings JSONserialization features to the ASP.NET web-services and allows calling web-services from client-side JavaScript, even using third-party JavaScript-libraries like jQuery.