Stephen Carrington talks about work that he and collaborators are undertaking to try and interrogate the complex array of carbohydrate structures present on mucin glycoproteins. These glycoproteins form part of the mucus gels that protect moist mucosal surfaces from microbial assault. Mucin glycoproteins can potentially act in two ways. Firstly, they can block the adhesins that are required for binding by harmful microbial pathogens to mucosal surfaces. Secondly, they can act as a food source for beneficial microbial colonisers that can compete with potential pathogens. We believe that these sugars represent a natural resource that can be mined for specific structures to be used to prevent harmful infections. This is because these structures represent the product of evolutionary drivers that lead to the construction of an effective barrier containing biologically engineered arrays of sugar structures that function in defense.