Valences are a very simple and yet powerful method of regulated rewriting. In this paper we give an overview on different aspects of this subject. We discuss closure properties of valence languages. It is shown that matrix grammars can be simulated by valence grammars over finite monoids. A Chomsky normal form theorem is proved for multiplicative valence grammars, thereby solving the open question of the existence of normal forms for unordered vector grammars. This also gives an alternative proof of the inclusion of context-free unordered vector languages in LOG(CFL). Moreover, we investigate valences in parallel systems, thereby solving part of open problems posted in [5, p. 267].