A novel Finite Word Length (FWL) controller design is proposed in the framework of a mixed It theory. A robust FWL controller performance measure is first developed, which takes into account the standard robust control requirements as well as the FWL implementation considerations, and the corresponding controller design problem is naturally reformulated as a mixed mu problem which can be treated effectively with the results of the mixed It theory. (C) 2009 Elsevier Ltd. All rights reserved.