In this chapter we present an overview and critique of the use of the modularity concept in evolutionary biology and psychology. It is shown that, at present, there are heuristic advantages in the modularity concept that allowed to show how a modular organization of genes helps to explain ontogeny and the evolutionary organization of genetic processes while evidence for large scale evolutionary processes leading to genetic modularity is mostly restricted to mathematical modelling. While biological module concepts and the idea of mental modularity are both motivated by evolutionary considerations, there still exists a wide gap between the two. Cognitive modules have been suggested by cognitive scientists and by psychologists, so far with varying success in providing empirical evidence. It is argued that a principal motivation to postulate cognitive modularity was to include evolutionary adaptation processes and their genetic encoding in the explanation of behaviour at the expense of learning. This is shown to be a short-sighted less than useful dichotomy because adaptation in social domains is more often than not based on genetically pre-conditioned opportunistic (learning) mechanisms even with many non-human species. It is further shown that social domain modules are not informationally encapsulated or mandatory, particularly if not being studied at the time of their ontogenetic appearance and that many cultural domains are equivalent to detector-indicator systems at a higher level than the individual. Consequences for a psychological concept of mental modularity are discussed and a frame of definition suggested.