The Threepenny Opera opens Wednesday night at the Loeb. This is the first in a series of offerings by the Harvard Summer School Repertory, a company that is traditionally proficient and thoroughly professional. The Bertolt Brecht play is a modern classic, and a delight to see if the performance is sufficiently raunchy. Kurt Weill's music and Brecht lyrics give the show its real flavor; "The Ballad of Mack the Knife" is the tastiest number. The Shark bites Wednesday and Thursday at 8 p.m. at the Loeb Drama Center, 64 Brattle St. Wednesday tickets are $4.95, a Thursday seat costs $5.95. Season series tickets are available at the Loeb.

Private Lives, a Noel Coward period piece about love and marriage, is being revived at the Tufts Arena Theater in Medford. The press release says that the show is "perfect summer entertainment," but so is rolling in the grass and what else is new? The play is set in the 1930s and presumably it's being milked for all the nostalgia it's worth. Any play that has a maid in it named Louise can't be all bad. Tuesday through Thursday at 8:15. General admission is $3.50, student tickets can be had for $2.

The Tempest will be alternating at the Publick Theater with Salome all summer long, beginning with a preview performance of the Shakespeare romance on July 4. The Publick Theater, 1175 Soldiers Field Road in Allston, is an outdoor arena and a pleasant place to see a good show if the weather and cast are cooperative. Bring your own seat and wait for some other night if the weather is threatening. Tickets are $2 cheap.

Sweet Eros will be playing Tuesday through Thursday at Cambridge's Theater Two if the police let the show go on. The show is about moral crisis, and on opening night it was closed down for "open and gross lewdness." Sounds good so far. Evidently the leading lady is strapped naked to a chair for 20 minutes of the performance, and, according to an ambitious Crimson reporter, is forced to copulate for 27 seconds. Quick thinking. It's not great drama, but performances are at 8 p.m. at 196 Broadway.

The Proposition is the only thing you really have to see while you're in Cambridge this summer. The Proposition is an improvisation group that is witty, clever and a joy forever. They play at 241 Hampshire St. in Inman Sq., every Wednesday through Saturday. Week night performances begin at 8:30 p.m. Tickets are $3 and $4, and there's a student rush.