A Nyquist-based frequency domain decentralized controller (DC) design technique for stability and guaranteed performance is proposed applicable for continuous-time systems described transfer function matrices. To guarantee stability and a required performance, interactions are included in individual designs using one selected characteristic locus of the matrix of interactions, further used to reshape frequency responses of decoupled subsystems and produce so-called equivalent subsystems [3]. Local controllers of equivalent subsystems independently tuned for stability and specified feasible performance constitute the resulting decentralized controller that guarantees specified performance of the full system. The developed frequency domain design procedure entitled Equivalent Subsystems Method is graphical, interactive and insightful. Theoretical conclusions are supported by simple examples illustrating step-by-step the DC design procedure.