What is the difference between patent assignment and licensing?

Patent assignment and licensing are two different ways of transferring patent rights. The MPEP defines assignment as:

‘Assignment of patent rights is defined as ‘a transfer by a party of all or part of its right, title and interest in a patent [or] patent application….”

In contrast, licensing is described as:

‘As compared to assignment of patent rights, the licensing of a patent transfers a bundle of rights which is less than the entire ownership interest, e.g., rights that may be limited as to time, geographical area, or field of use.’

The key difference is that assignment transfers ownership, while licensing grants permission to use the patent without transferring ownership.