This chapter begins with a description of the embryological development of the lower urinary tract, because it is during this development that the genes have their effect, and it is only by understanding this that we can appreciate how they do so. This is followed by description of genes and their protein products identified to be involved in various processes in the development, and how they interact. This involves cell signalling and gene regulation, and the effects on development if the genes are mutated. Different types of mutations are explained and the differences between mutations found so far in non-syndomic compared with syndromic VUR are described.