Antibody-dependent cellular cytotoxicity (ADCC) is a Fcγ receptor (FcγR)-mediated mechanism whereby virus-infected or transformed cells coated with antibody are lysed by immune cells expressing surface FcγRs. CD16, the FcγRIIIA, is essential for ADCC by NK cells, and is also expressed on a subset of human blood monocytes. Here, we report that human CD16-expressing monocytes exert ADCC in vitro as efficiently as NK cells. In the presence of specific antibodies, CD16+ monocytes had a broad spectrum of ADCC abilities and killed cancer cell lines and primary B lymphoma cells. Treatment with TLR agonists, DAMPs or cytokines such as IFNγ further enhanced the ADCC capacity of CD16+ monocytes. Monocytes lacking CD16 did not exert ADCC but acquired this property after CD16 expression was induced either by cytokine stimulation or transient transfection. Hence, CD16+ monocytes are important effectors of ADCC, a finding with important mechanistic and therapeutic implications.