The Massachusetts Town Vital Records Project
In the late 19th and early 20th centuries several towns and agencies compiled the vital records of over 200 Massachusetts towns and cities. The volumes combined town records, church records, private records, gravestone inscriptions and newspaper articles. They were published generally by the New England Historic Genealogical Society, but also by the Essex Institute and the Topsfield Historical Society, among others. These came to be known collectively as the "Tan Book" series, as the covers are tan in hard copy. They cover the time period from about 1600 to the end of 1849. (Death records, when taken from gravestones, sometimes are slightly later.)
These books are mostly out of copyright, and have been digitized by several efforts, including the volunteer Vital Records Project** (which has transcribed the books and makes them freely available), the NEHGS itself (which has digitized them into one database along with other pre-1850 records), and Footnote.com.
In addition, Ancestry has access to at least some of books both as part of the larger Massachusetts, Town and Vital Records, 1620-1988 database, and in older, index-only databases covering just births and marriages, respectively.
Note: Use this source only if you have no way of knowing which town book the record came from. Most of the repositories listed above either have the full series of separate books, or specify which book the material was transcribed from. The individual books each have their own source page on WeRelate (see the Tan Books category.)
The records were also digitized and expanded into CD-Rom volumes by county in the early 2000s.