High Quality Content by WIKIPEDIA articles! A defensive patent aggregation (DPA) is the purchasing of patents or patent rights to keep such patents out of the hands of entities that would assert them against operating companies. The opposite is offensive patent aggregation (OPA) which is the purchasing of patents in order to assert them against companies that would use the inventions protected by such patents (operating companies) and to grant licenses to these operating companies in return for licensing fees or royalties. OPA can be practiced by operating companies or Non-Practicing Entities (NPEs)