BOSTON, February 5, 2007 - State Street Corporation (NYSE: STT), the world's leading provider of financial services to institutional investors, announced today that it has signed a definitive agreement to acquire Investors Financial Services Corporation (NASDAQ: IFIN) in a stock transaction valued at approximately $4.5 billion. Each company's Board of Directors has approved the agreement. Upon closing of the transaction, State Street will enhance its position as a worldwide service provider of fund accounting to the mutual fund industry and its clear leadership in servicing for hedge and offshore funds.