AImtmct--One of the major obstacles to the routine exploitation of knowledge-based and expert systems, is the difficulty of validating the knowledge base, and of maimaining it in a state which reflects current knowledge. This is of particular importance for systems based on law or regulations, where it is vital that the knowledge base be a true reflection of the legal position, and where there is a constant stream of changes to the correct legal position. Maintenance Assistance for Knowledge Engineers (MAKE) is a project designed to explore these issues, and to build a set of tools which will support the validation and maintenance of knowledge bases deriving fi'om regulations. These tools include facilities to examine the structural features of the knowledge base, so as to guard against redundancy, nonprovability and comrudiction; facilities to identify parts of the knowledge base jeopardised by changes in the domain, or in the understanding of the domain; and facilities to perform a variety of "house keeping" tasks. The paperj~rstly analyses the different types of change that may be required to maintain the knowledge base, and then proceeds to describe the set of tools developed in the MAKE project to accommodate these changes.