Within truffe cultivation, some basic parameters are understood. For example, it is widely accepted that to cultivate black winter ‘Périgord’ truffles (Tuber melanosporum) we need a suitable climate, alkaline soils and host trees whose roots have formed mycorrhizal structures with T. melanosporum. Across the globe, these basic principles form the basis of truffle cultivation and an approach that is broadly successful. However, the very basic question of how a truffle forms and what triggers this development is still poorly understood. One of the most basic questions can be summarised in one word that has occupied humans for millennia: sex! In this blog post Prof. Paul Thomas discusses how DNA sequencing technology has led to the discovery that for the winter truffle there are two mating types (or ‘sexes’) and these must come together to form fruiting bodies (truffles).