CDIFF: a REDUCE package for computations in geometry of differential equations. The name ’CDIFF’ comes from the fact that the package allows to do computations with differential operators in total derivatives, i.e. C-differential operators, for differential equations in even and odd variables. The development of the package started in the early ’90s at the University of Twente by the following researchers: P. Gragert, Paul Kersten, G. Post, M. Roelofs. The ’Twente’ part of CDIFF has been recently included in the official REDUCE distribution on sourceforge. It can run on Linux and Windows, both 32-bit and 64-bit, as well as Mac OS. Recently, Raffaele Vitolo wrote new software in CDIFF package (latest version: 3.5 20/10/2013). It is devoted to computations concerning integrability related differential operators for general differential equations (i.e., not necessarily in evolution form) with an arbitrary number of independent variables. It can compute symmetries, conservation laws, Hamiltonian, symplectic and recursion operators, in local and nonlocal coordinates. It is distributed under the same free license of REDUCE.