The paper introduces the DeriNet lexical database, which includes more than 969,000 Czech words interconnected by 718,000 links corresponding to derivational relations (relations between a base word and a word derived from it). Derivational relations were identified by semi-automatic procedures and manual annotation. As the DeriNet network is fully compatible with a large inflectional dictionary of Czech (MorfFlex CZ), it can be used as a resource for an integrating approach to derivational and inflectional morphology of Czech both in linguistic research and in natural language processing.