Investors Bank & Trust or IBT was a custodian bank, and the principal operating subsidiary of Investors Financial Services Corp., a holding company based in Boston, Massachusetts. First founded in 1969 as an offshoot of Eaton Vance, the company was purchased by State Street Corporation in 2007 as an all-stock deal valued at nearly $4.5 billion and no longer operates as a separate listed company. State Street refers informally to the former IBT operation as "State Street Back Bay".