The development of reasoning systems that can reason and plan in a continuously changing environment is emerging as an important area of research in Artificial Intelligence. This paper describes some of the features of a Procedural Reasoning System (PRS) that enables it to operate effectively in such environments. The basic system design is first described and it is shown how this architecture supports both goal-directed reasoning and the ability to react rapidly to unanticipated changes in the environment. The decision-making capabilities of the system are then discussed and it is indicated how the system integrates these components in a manner that takes account of the bounds on both resources and knowledge that typify most real-time operations. The system has been applied to handling malfunctions on the space shuttle, threat assessment, and the control of an autonomous robot.