"JSON"'s range of data types is restricted BSON is optimised for parsing Or as the marketing spiel on the web site says: *Lightweight*: Keeping spatial overhead to a minimum is important for any data representation format, especially when used over the network. *Traversable*: BSON is designed to be traversed easily. This is a vital property in its role as the primary data representation for MongoDB. *Efficient*: Encoding data to BSON and decoding from BSON can be performed very quickly in most languages due to the use of C data types.