This paper reviews a number of recent developments in the field of nonlinear optics in resonant gas media, with a particular emphasis on phase-conJugate (PC) processes. The properties of PC emission via degenerate four-wave mixing (DFWM) are shortly reviewed: Doppler-free emission, dispersive character and directional anisotropy of the emission lineshape for saturating pumps, PC reflectivity in the saturation regime.

Recent extensions to optically thick gas media (*e. g.* Na vapor, near the D_{2} transition) have allowed one to reach PC reflectivities of the order of 200 %, and get PC self-oscillation. Higher-order contributions to the nonlinear susceptibility have been directly monitored via angle-resolved. phase-matched. degenerate multiwave mixing. This has been demonstrated in neon, where it has been possible to observe up to eleventh-order contribution.

On the other hand, non-degenerate wave mixing processes in resonant cascade three-level systems have allowed the observation of two-photon induced FWM (in Calcium), as well as dynamic Stark splitting of the emission lineshape in the saturation regime. Finally, novel ways for performing phase-conjugation with frequency up-conversion via non-degenerate, high-order multiwave mixing in a phase-matched backward geometry, are described.