The Cell Cycle Ontology (CCO) extends existing ontologies for cell cycle knowledge. CCO integrates and manages knowledge about the cell cycle components and regulatory aspects. This knowledge is assembled from a diverse set of already existing resources (GO, UniProt, IntAct, GOA, NCBI taxonomy, and so forth): the combination of the knowledge gives an overall picture of the cell division process. Not only enriched by the combination of resources, Ontology Design Patterns are being applied in CCO to provide a fine-grained and expressive knowledge model of the cell cycle.