In this paper, we study the design problem of multivariable PID controllers which guarantee the stability of the closed loop systems, H-2 or H-infinity performance specifications, or maximum output control requirement, respectively. Algorithms based on iterative linear matrix inequality technique are developed to find the feedback gains of PID controllers corresponding to the above mentioned four cases. A numerical example on the design of PID controllers for aircraft is provided to illustrate the effectiveness of the proposed method.