In order for UNEP to perform all of these functions, while retaining its role as the principal body within the United Nations system in the field of environment and taking into account the development aspects of environmental questions, it would require access to greater expertise and provision of adequate financial resources and it would require closer cooperation and collaboration with development and other relevant organs of the United Nations system. Furthermore, UNEP's regional offices should be strengthened without weakening its headquarters in Nairobi, and UNEP should take steps to reinforce and intensify its liaison and interaction with UNDP and the World Bank.