PRECO is a two-component exciton model code for the calculation of double differential cross sections of light particle nuclear reactions. The code, written in FORTRAN, runs on a PC and calculates the emission of particles up to mass four, including separate subroutines for nucleon transfer reactions, knockout and inelastic scattering involving complex particles, and collective state excitation (both discrete and GDR). Emission of a second nucleon at either the preequilibrium or equilibrium phase of the reaction is allowed following neutron or proton emission. Available options include collective or ordinary pairing corrections, isospin conservation, and shell structure effects. Output of both the energy differential and double differential cross sections is available. A recommended set of global parameters is provided.