As part of research on sophisticated control for sensor interpretation, a planning-based control scheme for blackboard systems is developed. A planner's goal/plan/subgoal structure provides explicit context information that can be used to index and apply large amounts of context-specific control knowledge. The key obstacle to using planning for the control of problem solvers is the need to deal with uncertain and dynamically changing situations without incurring unacceptable overhead. These problems are addressed in several ways: the authors' planner is script-based, planning and execution are interleaved; plans can invoke information gathering actions; plan refinement is controlled by plan-specific focusing heuristics; and the system's focus of attention can be dynamically shifted by the refocusing mechanism. Refocusing makes it possible to postpone focusing decisions and maintain the opportunistic control capabilities of conventional blackboard systems. Planning with refocusing results in a view of the control process as both a search for problem solutions and a search for the best methods to determine these solutions.>