This paper presents a field study of decision-making processes at two organizations operating in high-velocity environments. It reviews existing literature on managerial knowledge structures and decision-making, and identifies methodological and conceptual limitations with these approaches with respect to organizations in high-velocity environments. The authors develop two interpretive cases that focus on the articulated and social methods management teams used to make decisions. They found that both organizations used rules of thumb or heuristic reasoning in their decision-making, that these rules of thumb functioned as headlines of deeper organizational narratives, and that these narratives were grounded in emotional as well as purely rational considerations. They suggest that the term 'guiding principle' usefully integrates their three findings into a second-order concept that may be further explored in future research of both a descriptive and prescriptive nature. Copyright © 2005 SAGE Publications.