This bookcontainsthe essence ofthepapersand the discussions from a twoweek longAdvanced Study Institute (ASI) held in September 1985. The idea ofhaving an ASIaboutthe topic ofIntelligent Decision Support (IDS) systems goes back to a NATO workshop on Human Error held at the Rockefeller Center in Bellagio, Italy, in September 1983 Ina way it goes even furtherback sincethe Bellagioworkshop continueda seriesof NATOASls and workshops on advanced human-machine systems thatstarted adecadeagoin 1976. The present ASI therefore represents neitherabeginning noranend, but is rather a snapshot ofthefrontiers of thinking about man-machinesystemsas they looked in 1985. One problem that was important in 1983, and which remains so today, was to improve the understanding of human decision making and behaviour in particularly demanding applications, such as thecontrol of complexindustrial processes. Oneway of tryingto solve this problemwasto organise a high-level meeting where the relevant different scientific disciplines could converge and interact. Consequently three of the participants in the Bellagio workshop- Erik Hollnagel, Giuseppe Mancini, and David Woods, supported by a technical programme committee consisting of Don Norman, Jens Rasmussen, James Reason, and GiuseppeVolta - undertook to prepare and direct such a meeting. During the initial discussions the topic of the meeting was defined to be the application of intelligent decision aidsin process environments, and this in turnbecamethe title of the ASI.