Disclosed are compositions that include anti-CD74 immunoconjugates and optionally a therapeutic and/or diagnostic agent. In preferred embodiments, the immunoconjugates comprise one or more anti-CD74 antibodies or antigen-binding fragments thereof, conjugated to a carrier such as a polymer, nanoparticle, complex or micelle. Also disclosed are methods for preparing the immunoconjugates and using the immunoconjugates in diagnostic and therapeutic procedures. In certain preferred embodiments, the therapeutic methods comprise administering to a subject with a CD74-expressing disease an anti-CD74 immunoconjugate and thereby inducing cell death of CD74-expressing cells. In more preferred embodiments, the CD74 immunoconjugate is capable of inducing cell death in the absence of any other therapeutic agent, although such agents may be optionally administered prior to, together with or subsequent to administration of the anti-CD74 immunoconjugate. The compositions may be part of a kit for administering the anti-CD74 immunoconjugates or compositions.