Maintaining regulatory compliance is an increasing concern. Legal Knowledge Management systems could support the work of compliance managers. However, there are challenges to overcome, of interpreting legal knowledge and mapping it onto business processes. In this discussion paper we determine requirements for Legal Knowledge Management systems that can handle these challenges. We argue that an approach to Legal Knowledge Management should consist of four pillars: (1) a legal ontology to express the legal concepts that are central to the interpretation of rules and regulations in practice, (2) natural language processing techniques, to semi-automatically populate the ontology, (3) a systematic method for mapping the legal concepts onto the actual data and business processes of a company, and (4) a method to construct an audit trail as part of the process design, providing legally acceptable evidence of compliance. The challenges are illustrated by an example of MIFID, a set of European regulations in the financial domain.