Psoriasis and psoriatic arthritis have been recognized for more than 100 years. Neither the link between psoriasis of the skin or nails and arthritis of the joints nor the pathogenesis of either condition alone or in combination has yet been explained. Our understanding of the mechanisms of inflammation of the skin and the joints has improved over the past 30 years and there are some interesting common threads of knowledge that may bring us closer to understanding psoriasis and psoriatic arthritis. This article will explore further the areas of immunogenetics, infection, autoimmunity, vascular morphology/angiogenesis, trauma and the nervous system in respect of psoriasis and psoriatic arthritis highlighting in particular those aspects that previously have not received due reference.