Invariant natural killer T (iNKT) cells are an innate T-cell lineage known to recognize a range of endogenously derived and exogenously derived glycolipid antigens. Advances in our understanding of this T-cell subset have enabled researchers to investigate the immunomodulatory activity of iNKT cell ligands in experimental models of diseases such as cancer, allergy and chronic inflammatory joint disease. To a large extent, the ability of iNKT cells to regulate such disease models has been ascribed to their capacity to promote a polarized cytokine environment, which is understood to skew adaptive immune responses. In this Review, we discuss the current understanding of how iNKT-cell polarization is regulated and relate this basic theory to the proposed role for iNKT cells in models of rheumatologic disease.