It is now well documented that carbohydrates play multiple roles in biological processes, and hence are interesting targets for chemical biology and medicinal chemistry programs. This review focuses on a subset of carbohydrates, specifically sialic acid containing carbohydrates. It highlights their occurrence and diversity, and presents evidence for their roles in a range of biological pathways. It illustrates that they are targets for novel medicinal chemistry strategies for a range of therapeutic areas, including cancer and immunity. Case studies highlight opportunities and challenges in this area, and sialic acid-based drugs that have entered clinical practice and are promising candidates for future disease intervention schemes, are discussed. The review concludes by highlighting perspectives and emerging roles for these targets.