Targeted therapies using nanoparticles have been proposed to address some drawbacks of conventional chemotherapy. In the last two decades, surface modification of nanoparticles with antibody ligands has been extensively explored for the safe and effective delivery of chemotherapeutic drugs. By capitalizing on receptors overexpressed on cancer cells or angiogenic endothelial cells, antibody-functionalized nanoparticles are promising candidates to improve selectivity for target cells and, thus, therapeutic efficacy. This work offers a brief overview of nanotechnology applied to targeted cancer therapies and highlights the use of antibodies as targeting ligands. After presenting a summary of the most common methods for nanoparticle functionalization with antibodies, the authors discuss different targeting strategies divided into angiogenesis-associated targeting, uncontrolled cell proliferation targeting, and tumor cell targeting. Special emphasis is given to antibody-nanoparticle conjugates that have entered the clinical testing phase. Some explanations for the discrepancy between preclinical and clinical observations are also provided.