C#

Right click on the project name in your solution browser, and select 'Add Existing Item'. Select the class file and it will be added to your project. You can either change the namespace of the class to your current project's namespace, or reference it using the existing namespace. Here's an example, assuming the class name is MyClass, and the old namespace is MyNamespace, and also that you have added it to the project: MyNamespace.MyClass myClass = new MyNamespace.MyClass(); myClass.DoSomething(); If you change the namespace to your current project, you won't have to prefix the class calls with "MyNamespace".