In recent years, expert systems technology has become commercially mature, but widespread delivery of systems in regular use is still slow. This thesis discusses three main difficulties in the development and delivery of expert systems, namely,the knowledge acquisition bottleneck, i.e. the problem of formalizing the expert knowledge into a computer-based representation.the migration problem, where we argue that the different requirements on a development environment and a delivery environment call for systematic methods to transfer knowledge bases between the environments.the user acceptance barrier, where we believe that user interface issues and concerns for a smooth integration into the end-user’s working environment play a crucial role for the successful use of expert systems.In this thesis, each of these areas is surveyed and discussed in the light of experience gained from a number of expert system projects performed by us since 1983. Two of these projects, a spot-welding robot configuration system and an antibody analysis advisor, are presented in greater detail in the thesis.