Many expert systems implementations are unsuccessful: the system falls into disuse or is not used to the extent originally envisioned. This paper reports on a study on the factors that lead to successful (or conversely less successful) expert system implementation. Six cases, drawn from three high-technology companies, were investigated: three very successful, three less so. Following analysis of the cases, propositions were developed regarding various success factors and their interrelation. We found that top management support and immediate manager acceptance are important, and that demonstrable business benefits and problem urgency affect management support. At the user level, perception of management support, degree of organizational change, organizational support, and users' personal stake in the system affect operational use. We relate our findings to what is known about implementation in Management Science and Information Systems, concluding that successful expert systems implementation exhibits properties found in both.