Porcine circovirus type 2 (PCV2) was first sporadically identified in pigs with postweaning multisystemic wasting syndrome (PMWS) in Canada in the mid 1990's. Epidemics of severe systemic disease associated with PCV2 were subsequently identified in Europe and Asia followed by North America. The widespread use of commercial vaccines has effectively controlled PCV2-associated disease (PCVAD) which includes PMWS, pneumonia, porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. Retrospective studies have demonstrated that PCV2 circulated unnoticed in swine for decade's prior widespread clinical disease. A shift in dominant genotype from PCV2a to PCV2b appeared correspond to severe PCVAD. Recently, a new species of circovirus, termed porcine circovirus type 3 (PCV3), was identified from sows with clinical symptoms normally associated with PCV2 infection as well as in aborted fetuses.