This paper explores diachronic change in word-formation. The phenomena of change usually attributed to the domain of word-formation range from phonological alterations of affixes, grammaticalization and the extraction of word-formation elements out of loans to the extinction of word-formation patterns due to the loss of morphological productivity. But actually, these phenomena affect different levels of word-formation, i.e. word-formation products, word-formation patterns and the word-formation system as a whole. Some of them are not even restricted to word-formation but do apply to other components of grammar as well. In this paper I will argue that the only kind of change that is specific to the domain of wordformation is the change of word-formation constraints. This change of constraints is reflected in changes of morphological productivity. Empirical evidence for this connection will be drawn from a corpus-based diachronic study of German -er-nominalization.