Today's the preliminary in Boston, Somerville, Medford and other assorted cities, so if you haven't voted early or by mail, today's your last chance to help decide who gets on the November ballot.
At least in Boston, there have been some changes in the locations of polling places, so know before you go. If you're not sure where to vote, the state has a lookup system.
Not sure whom to vote for? Progressive MA sent questionnaires to the candidates for mayor and city council in Boston (both at large and at the district level). The Dorchester Reporter has overviews of the 17 at-large candidates (you get to vote for up to four of them).