Inline ASP.NET Tags Differences <%#, <%, <%=, <%$, <%--, <%@

It gets confusing at times when figuring out which ASP.NET tag is best to use. Moreover, it is good to know the settle difference between a couple of the similar tags. One might think that for example the "<%#" tag and "<%=" are the same for certain cases and can be used interchangeably. Actually they are different and in most cases only one of them would work unless some code change is done. So here is a summary of the tag attributes and the differences amongst them:

<% ... %>

This tag is used to insert code into an ASP.NET page usually with a .aspx extension. One of the most common use of this tag is conditional statements where you can choose to display certain content only when a condition is met.

<% if(isLoggedIn){ %>
   Hello user
<% } else { %>
   Please login
<% } %>

For more info:
http://msdn.microsoft.com/en-us/library/ms178135(vs.80).aspx

<%# ... %>

This tag is used with data binding. It can be used with DataBinder.Eval() or DataBinder.Bind() or just with any protected or public member as shown in the example. The trick about this tag is that it must be used inside a server-side element (with runat="server"). Also the DataBind() method of that element must be called at some point. However, certain ASP.NET elements automatically call their DataBind() method in their PreRender() methods. So there is no need to is explicitly call their DataBind() methods. Such elements are GridView, DetailsView, and FormView.

<div id="div1" runat="server">
   Hello <%# userName %>
</div>

In the code behind:

protected void Page_Load(object sender, EventArgs e)
{
   div1.DataBind();
}

For more info:
http://msdn2.microsoft.com/en-us/library/ms178366.aspx

<%= ... %>

This tag is similar to the above tag in the sense that it is used to evaluate the value of a protected or public member variable. The tag evaluates the ToString() method of the variable used and displays it. The nice thing about this tag is that it does not need to be inside a server-side element and its parent element does not even need to have a name.

<div>
   Hello <%= userName %>
</div>

For more info:
http://msdn.microsoft.com/en-us/library/6dwsdcf5(VS.71).aspx

<%$ ... %>

This tag is used to evaluate expressions in a configuration file. It is usually used for connection strings but it can be used with AppSettings and other configurations.

<asp:SqlDataSource ID="SqlDataSource1" Runat="server" 
    SelectCommand="SELECT * FROM [Employees]"
    ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString1 %>">
</asp:SqlDataSource>

For more info:
http://msdn.microsoft.com/en-us/library/d5bd1tad.aspx

<%@ ... %>

This is usually used at top of a page as a directive to register controls or import a library.

<%@ Register TagPrefix="uc" Namespace="MyCustomUserControl" %>

For more info:
http://msdn.microsoft.com/en-us/library/xz702w3e(VS.80).aspx

<%-- ... --%>

This tag allows you to add server-side comments which would never show in the HTML output. This is different from using an HTML comment (<! -->) because HTML comments do get rendered in the outputted HTML.

<%-- this is a comment --%>

For more info:
http://msdn.microsoft.com/en-us/library/4acf8afk.aspx

That should be a good summary but there is obviously more to some of tags.