We describe a task-oriented approach to guideline modeling that we have been developing in the EON project. We argue that guidelines seek to change behaviors by making statements involving some or all of the following tasks: (1) setting of goals or constraints, (2) making decisions among alternatives, (3) sequencing and synchronization of actions, and (4) interpreting data. Statements about these tasks make assumptions about models of time and of data abstractions, and about degree of uncertainty, points of view, and exception handling. Because of this variability in guideline tasks and assumptions, monolithic models cannot be custom tailored to the requirements of different classes of guidelines. Instead, we have created a core model that defines a set of basic concepts and relations and that uses different submodels to account for differing knowledge requirements. We describe the conceptualization of the guideline domain that underlies our approach, discuss components of the core model and possible submodels, and give three examples of specialized guideline models to illustrate how task-specific guideline models can be specialized and assembled to better match modeling requirements of different guidelines.