Find Types in All Assemblies

There are two steps to achieve this:

• The AppDomain.CurrentDomain.GetAssemblies() gives you all assemblies loaded in the current application domain.
• The Assembly class provides a GetTypes() method to retrieve all types within that particular assembly.

Hence your code might look like this:

foreach (Assembly a in AppDomain.CurrentDomain.GetAssemblies())
{
    foreach (Type t in a.GetTypes())
    {
        // ... do something with 't' ...
    }
}

To look for specific types (e.g. implementing a given interface, inheriting from a common ancestor or whatever) you’ll have to filter-out the results. In case you need to do that on multiple places in your application it’s a good idea to build a helper class providing different options. For example, I’ve commonly applied namespace prefix filters, interface implementation filters, and inheritance filters.

For detailed documentation have a look into MSDN here and here.