Microbial surfaces are decorated with carbohydrate (glycan) structures that play important structural roles and also mediate interactions with the host. In particular, cell-surface microbial glycans often modulate the innate immune system and are potent inducers of antibody responses. The latter role has made them attractive targets for exploitation in vaccine and diagnostic development and there are now several commercial successes in this area. While such applications often involve the use of glycans isolated from natural sources, the heterogeneity of such materials and the generally tedious isolation procedures have motivated efforts to use materials obtained by chemical synthesis, which are homogeneous and which can be produced at scales that enable vaccine and diagnostic use. In this talk, I will present two stories on the use of synthetic glycans: one describing their role in studies leading to an improved urine-based TB diagnostic and the other their use in developing a vaccine for Streptococcus suis, an important swine pathogen that is also zoonotic.