Ontologies are shared formal conceptualizations of specific domains. They serve as foundations for knowledge representation and reasoning as well as standards for information exchange and interoperability. This White Paper gives a concise overview on the challenges of developing and applying ontologies for supporting crisis management. Firstly, we will introduce fundamental concepts related to ontologies and knowledge engineering. Then, we will discuss the role ontologies play for (a) enabling probabilistic and causal reasoning, (b) defining interoperability solutions and (c) creating a resilience data space. Thereafter, we will review a selection of existing resources and their reusability. Finally, we will conclude and give recommendations on further work.