Reliability and acceptance of intelligent completions has increased dramatically over the last decade. With this, there has been a demand to push the limits of intelligent completion technology to allow access to more zones at higher pressures and temperatures while minimizing cost and maximizing reliability. Meeting this demand not only requires flow control components such as packers or Interval Control Valves (ICV) but it also requires a system and methodology to control those components. Different control methodologies have been designed and tested over the years using hydraulic power, electric power, or combinations of the two. These hydraulic and electric requirements have been supplied by small diameter metal hydraulic control lines and metal-encased electrical conductors. Control and power requirements to the downhole components have increased as operators have desired control of more zones. Downhole control system requirements have become increasingly demanding to meet these requirements. This paper discusses the history and future of control systems for intelligent completions. It describes how these systems have evolved from simple hydraulic systems to more complex multiplexing systems and presents the advantages and disadvantages of each.