The functional integral formalism is used to provide a unified treatment of the effect of squeezing of the bath and frequency modulation of the system-bath coupling on the decoherence and dissipation properties of an open quantum system. The system chosen is a standard one consisting of a particle in a harmonic oscillator potential interacting with a bath of harmonic oscillators by a coupling of the position-position kind. Using an Ohmic bath and the high-temperature limit, the coefficients of the master equation describing dissipation and decoherence are obtained and analyzed. © 2004 Elsevier B.V. All rights reserved.