A transformation-based approach for the full and partial input-output decoupling of square and overactuated linear systems is presented. A certain transformation is introduced which highlights the coupling effects of the system. Based on the transformed system matrices, it can simply be seen how full and partial decoupling is derived. Additionally to the square case, an analysis for overactuated systems is given and it is highlighted how the degrees of freedom coming from overactuation can be used to manipulate the decoupling result. The contribution of the paper is to present an easy to handle decoupling technique which enables a simple access to input-output decoupling and visualizes all degrees of freedom.