Psoriasis is a chronic inflammatory skin disorder that affects about 2-3% of the population. It is triggered by the immune system, and new insights into the immune processes have thrown up a number of exciting drug targets. This Nature Reviews Drug Discovery animation explores how the immune system goes awry in psoriasis and illustrates how agents that target the cytokine interleukin 17, or other players in the same pathway, are being developed into novel therapies for psoriasis.