Many efforts in knowledge acquisition are designed from a knowledge engineer's perspective and as a consequence fall short of allowing experts to elaborate successfully their own situated knowledge. Knowledge engineering approaches are typically not user-centered and consequently are often the cause of a bottleneck in system development. This paper describes and evaluates the Advanced Knowledge And Design Acquisition Methodology (AKADAM) project as an attempt to overcome such inadequacies by provision of user-centered knowledge acquisition techniques. Both theoretical and practical issues are examined. The role of multiple perspectives (i.e. "knowledge as rules", "knowledge as concepts", and "knowledge as designs"), their relationship to a user-centered approach, and the necessity of flexible knowledge integration are portrayed by applying AKADAM to a complex, real-world domain (i.e. the development of an electronic associate for fighter pilots). Results suggest that this approach is capable of providing: (a) a naturalistic knowledge elicitation environment endorsed by users, (b) an externalization of experts' intuitive knowledge in a form which is similar to their own mental representation and (c) an integrated, large-scale knowledge set suitable for infusing knowledge into AI architectures and human-computer interface design.