A method for robust decentralized controller design of continuous and discrete-time controllers for SISO and MIMO systems is proposed. The uncertain MIMO system is given by a set of square transfer matrices of any dimension. The design procedure relies on the Equivalent Subsystems Method (ESM) - an independent design of local controllers for stability and required performance of the overall system. The ESM has been extended by integrating robust stability conditions directly in the independent design of local controllers to obtain a unified robust decentralized controller design method. To demonstrate the design procedure, a discrete-time robust decentralized PID controller for a minimum-phase system was designed. (C) 2019 Elsevier Ltd. All rights reserved.