Massachusetts Congressional Districts have been redrawn as a result of the 2010 Census.
This map shows the old Massachusetts Congressional districts through the 112th Congress, which serves through the end of 2012. (Note: District 5 is now represented by Niki Tsongas, not Martin Meehan, but the district lines are still the same.)
This map shows the new congressional districts which were adopted by the Legislature in November 2011. They will be effective starting with the 113th Congress, which will be elected in November 2012 and serve starting in January 2013. A smaller version of the new map is shown below.
If you can't tell which district you are in from the map, use this tool provided by the House of Representatives.