Sheet and film processes, which include papermaking, polymer film extrusion, and adhesive coating, are of substantial industrial importance. The processes are poorly conditioned and truly large scale, with up to hundreds of manipulated variables and thousands of sensor locations. The uncertainties in sheet and film process models require that they be explicitly taken into account during the control design procedure. Numerically efficient algorithms are developed that provide robust optimal controllers for a wide variety of uncertainty descriptions. The robust optimality of the controllers can be relaxed to provide low order controllers suitable for real time implementation. Robust controllers are designed for a simulated paper machine, based on a realistic description of the interactions across the machine, and the level of model inaccuracies. (C) 2001 Elsevier Science Ltd. All rights reserved.