Troizinia (Greek: Τροιζηνία) is a municipality in the Islands regional unit, Attica, Greece. The seat of the municipality is the town Galatas.
The municipality Troizinia was formed at the 2011 local government reform by the merger of the following 2 former municipalities, that became municipal units (constituent communities in brackets):
The province of Troizinia (Greek: Επαρχία Τροιζηνίας) was one of the provinces of the Piraeus Prefecture. Its territory corresponded with that of the current municipalities Troizinia and Poros. It was abolished in 2006.