The process of forward stimulated Brillouin scattering in standard single-mode fibers is described. The analysis brings together the electrostrictive stimulation of guided acoustic modes by a pair of co-propagating optical fields and the photoelastic scattering of the same two optical fields by the acoustic wave. The propagation of the optical fields is formulated in terms of nonlinear polarization components and coupled nonlinear wave equations. The solutions to the equation signify the coupling of optical power from the higher-frequency optical wave component to the lower-frequency one. Coupling is quantified by a nonlinear coefficient, with units of W−1 × m−1, the same one that was found earlier to describe spontaneous scattering processes. The stimulated Brillouin scattering between the pair of tones is also associated with the generation of spectral sidebands of increasing orders. The Brillouin scattering contributions add up with those of Kerr effect four-wave mixing terms.