Cannabis in Massachusetts is legal for medical and recreational use. It also relates to the legal and cultural events surrounding the use of cannabis. A century after becoming the first U.S. state to criminalize recreational cannabis, Massachusetts voters elected to legalize it in 2016.

In 2008 Massachusetts voters decriminalized the possession of small amounts of marijuana. Massachusetts became the eighteenth state to legalize medical marijuana when voters passed a ballot measure in 2012, even though the federal government still lists marijuana as a Schedule 1 controlled substance with no medical value. Recreational marijuana is legal in Massachusetts as of December 15, 2016, following a ballot initiative in November of that year.

As of 2010 almost 10% of Massachusetts residents over the age of 12 had used marijuana in the past month, and almost 16% had used marijuana within the past year. The largest event for the support of the legalization of marijuana, the Boston Freedom Rally, which draws thousands of attendees from all over the region, takes place every year in September.