With the Transaction API, you can obtain information about transactions (adds, drops, trades, and league settings changes) performed on a league. A transaction is identified in the context of a particular league, although you can request a particular Transaction Resource as the base of your URI by using the global transaction_key. A user can only retrieve data about a transaction if that user is part of a private league of which the user is a member, or if it's in a public league.
TODO: additional methods for creating transctions