Psoriatic arthritis (PsA) is characterised by several unique clinical features that differentiate it from rheumatoid arthritis (RA). Attempts to identify immunopathological mechanisms, some shared with psoriasis, that underlie these differences from RA have been most challenging. Recent research studies, however, highlight novel findings in PsA at the molecular, cellular, and tissue levels that form the basis for a new understanding of this relatively common form of inflammatory arthritis. In particular, the availability of new, biological antitumour necrosis factor α therapies have allowed further insight into the immunopathology of psoriasis and PsA. This brief review focuses on immunohistological studies in psoriatic skin, PsA synovium, and bone to demonstrate how these data advance our knowledge of disease pathogenesis.