The present disclosure relates to a class of engineered polypeptides having a binding affinity for interleukin-17A (IL-17A), and provides an IL-17A binding polypeptide comprising the sequence EX2DX4AX6X7EIX10X11 LPNL X16X17X18QX20X21AFIX25 X26LX28X29. Also disclosed is the use of such an interleukin-17A binding polypeptide as a diagnostic, prognostic and/or therapeutic agent.