Disclosed are antibodies, including antibody drug conjugates, that specifically bind to NTB-A. Also disclosed are methods for using the anti-NTB-A antibodies to detect or modulate activity of (e.g., inhibit proliferation of) an NTB-A-expressing cell, as well as for diagnoses or treatment of diseases or disorders (e.g., cancer) associated with NTB-A-expressing cells. Further disclosed is a method of treating multiple myeloma using an anti-NTB-A antibody drug conjugate, which optionally includes an anti-NTB-A antibody as disclosed herein.