 <p>A module contains IL and many of them are linked together to create an assembly, which is usually housed in a PE like a .exe or a .dll.</p> <p>A PE can contain native (non managed) code as well.</p> <p><a href="http://en.wikipedia.org/wiki/Portable_Executable" rel="nofollow noreferrer">This is a good intro to the concepts.</a></p>