A heterotetrameric AP-type membrane coat adaptor complex that consists of alpha, beta2, mu2 and sigma2 subunits, and links clathrin to the membrane surface of a vesicle, and the cargo receptors during receptor/clathrin mediated endocytosis. Vesicles with AP-2-containing coats are normally found primarily near the plasma membrane, on endocytic vesicles. In at least humans, the AP-2 complex can be heterogeneric due to the existence of multiple subunit isoforms encoded by different alpha genes (alphaA and alphaC). [ http://www.ncbi.nlm.nih.gov/pubmed/10611976 http://www.ncbi.nlm.nih.gov/pubmed/22022230 http://www.ncbi.nlm.nih.gov/pubmed/21097499 http://www.ncbi.nlm.nih.gov/pubmed/24322426 ]