The Boston Archdiocese Archives is located in Braintree, MA. If your family is Catholic, or your genealogy research has revealed that there are some Catholic ancestors in your family tree, you might want to search through this vast archive. It is going to be especially useful to genealogists whose Catholic ancestors came from the Boston area, and lived there from the early 1900's to the 1930's.
The official sacramental records that are stored in this archive are going to reveal a lot of information that is useful to genealogists. Sacramental records are official documents that contain information about the people involved in a baptism, marriage, first communion, or confirmation. Each of those sacraments is an important milestone for a Catholic. There are also some death, burial, and cemetery records located in this archive, but there are very few of those. Sacramental records might state who an ancestor's parents were, who they married, and more.
You can access sacramental records that predate 1930. This is because the archive is following the U.S. Census privacy guidelines. Those guidelines state that information like the kind found on the sacramental records cannot be publicly released until 72 years after the the date it was recorded.
For best results, you should find out some key information about your Catholic ancestors before you visit the Boston Archdiocese Archives. This is because the records are, for the most part, hand written into ledgers or notebooks that were used to record baptisms. The ledgers are not indexed in any way at all. There is no central index of the records that are located in this archive. This is not the kind of situation where knowing an ancestor's name is going to instantly provide you with the information you seek.
What neighborhood did your ancestor live in? It may be possible to extrapolate what parish they belonged to based on where they lived, but this isn't always true. Narrowing down what parish you should start searching through can be a helpful. It's useful if you know the name of the priest who officiated the marriage, baptism, or other sacrament. For more details about how to search, and what kinds of record are available, visit the website for the Archives of the Archdiocese of Boston.