Wolf-Rayet (WR) stars and their possible precursors, the Luminous Blue Variables (LBVs), are often surrounded by ring nebulae. It is believed that these nebulae are formed by the action of the stellar wind, matter being ejected from the star in the past, or a combination of these two processes. The various research applications of LBV and WR nebulae are reviewed with regard to the information they provide on the properties of the central stars. They are very useful probes of stellar evolution since the details of the previous evolutionary phases of the central stars are contained in the nebulae. In particular, abundance studies can provide insights into the chemical processes operating during the precursor phases. The nebulae can also be used as probes of the far-UV ionizing flux distribution of the central WR stars by comparing the observed levels of nebular ionization with those produced with non-LTE WR model flux distributions. Comparisons of stellar effective temperatures and luminosities derived using this technique with those determined by modelling stellar emission lines can identify deficiencies such as the lack of line-blanketing in WR model atmospheres. Very hot WR stars can also be identified by searching for nebular HeII emission. Studies of bipolar structures in LBV and WR nebulae provide valuable clues on wind asymmetries in the central stars.

Multi-wavelength investigations of the interstellar environment around WR stars using IUE, IRAS, and optical data have led to the discovery of extended shells of gas and dust 50-100 pc in diameter in the lines of sight to the WR stars HD 50896, HD 96548, and HD 192163. These three stars share several common characteristics: (1) associated N- and He-enriched ring nebula, (2) spectral class WN5-8, and (3) spectral and photometric variability. Surveys of IUE spectra and IRAS images reveal a few additional candidates for such extended shells. Although positional coincidences cannot be excluded, possible origins of these extended shells include interstellar bubbles formed by stellar winds, non-conservative mass loss from binary systems, and supernova remnants. Current data suggest these three stars may be in a post X-ray binary stage, representing the second WR phase of massive binary star evolution. The discovery of extended shells of gas and dust possibly related to WR stars is important because the search for stars in the second WR phase, after the supernova of the primary, has been quite elusive. However, the observational evidence and available theoretical models for post-supernova massive binary star evolution and subsequent non-conservative mass transfer are not yet sufficient to firmly identify the origins of these extended shells.

We present 2D numerical simulations of evolving ring nebulae around moving Wolf-Rayet stars. We have considered the interaction of the fast WR wind with the circumstellar matter modified by the previous action of the slow RSG wind. The resulting shell morphology is far from spherical and shows scallops due to several kinds of instabilities. The exact appearance of the ring nebula depends on the value of several parameters such as the unperturbed medium density and the velocity of the star.