Siglecs are sialic-acid-binding immunoglobulin-like lectins involved in cell-cell interactions and signalling functions in the haemopoietic, immune and nervous systems, Significant advances have been made in our understanding of the link between carbohydrate recognition and signalling for two well-characterised siglecs, CD22 and myelin-associated glycoprotein. Over the past few years, several novel siglecs have been discovered through genomics and functional screens. These 'CD33-related' siglecs have molecular features of inhibitory receptors and may be important in regulating leucocyte activation during immune and inflammatory responses.