Abstract. In this paper we present, the Maple package Cadecom which is designed for performing computations in rational function fields. The main objects that Cadecom deals with are multivariate rational functions over any computable field, and the key tool are the functional decomposition algorithms. The functional decomposition problem has many applications in computer science, engineering (CAGD), pure mathematics or robotics. We motivate the interest of this program package by presenting applications on computing roots, simplifying sine-cosine equations, integrating rational functions, computing subfields, computing Grobner bases and reparametrizing parametric curves. We also include a short overview of the package from the Maple system point of view.