This paper proposes the open reactive dispatching mechanism, where predicates are not only used for determining the applicable procedure to execute for the current situation but also for ensuring that the entire procedure execution happens under the specified predicate. Predicates operate on contextual parameters whose values change continuously (e.g., the current user's location). The dispatching process is repeated whenever the values of contextual parameters change. As a result previously unsatisfied predicates may later become satisfied and their associated procedures are selected for execution. Additionally, new procedures can be added at runtime and become part of the potential procedures that the dispatching process can select from. The open reactive dispatching mechanism is embodied in the Flute language, a proof-of-concept programming language that is designed for context-aware applications.