This special issue provides information on current and future research directions in the emerging field of Decentralized Control of Large Scale Complex Systems. There is generally adopted view that a dynamic system is large scale complex whenever it is necessary to partition its analysis or synthesis problem to manageable subproblems. Its fundamental characteristics in modeling and control are high dimensionality, uncertainty, information structure constraints, and delays. Theory of large scale complex systems is based on several new ideas, where most of them belong to one of three design concepts. System decomposition, decentralized control, and robustness and approximation have been and are being elaborated as powerful tools to overcome difficulties caused by particular properties of these systems. The theory was initiated and developed in the 1970s and 1980s mainly for the linear time-invariant systems. Large scale complex systems gave rise to problems that were well known in multivariable system theory but have not been solved satisfactorily. There is a renewed emphasis on decentralized control systems today. The changes in the scope and implementations of control systems are motivated by strongly increasing complexity of current control design problems as well as technology driven changes. Such changes are primarily made possible by network control systems and low cost processors. There is some reordering of today's priorities leading to the emphasis on the explicit consideration of the interconnections and decentralized control systems in control system analysis and design.