To clarify: User Controls: - Are basically ASP.NET's version of include files (except that they support properties and events) saved as .ascx. Cannot be easily shared among projects. - Cannot be added to toolbox. Custom Controls are not written "in html only". They are written in code and compiled to a .dll.

User controls:-

1. These controls are specific to our appication it self. i.e,  We can   not use in multiple applications.

2. It supports drag & drop the controls from the toolbox.

3. These controls does not added to the toolbox.

Custom COntrols:-

1. These controls are specific to all appication. i.e,  We can use in multiple applications by adding the .dll in u r application.

2. It does not supports drag & drop the controls from the toolbox. To create custom controls we have to write the code in html only.

3. These controls will be added to the toolbox.

web control build with html code only but where as Custom control need to writte server side code also