*Review* **The Wolf–Rayet Content of the Galaxies of the Local Group and Beyond**

**Kathryn Neugent 1,2,\* and Philip Massey 2,3**


Received: 12 July 2019; Accepted: 17 August 2019; Published: 21 August 2019

**Abstract:** Wolf–Rayet stars (WRs) represent the end of a massive star's life as it is about to turn into a supernova. Obtaining complete samples of such stars across a large range of metallicities poses observational challenges, but presents us with an exacting way to test current stellar evolutionary theories. A technique we have developed and refined involves interference filter imaging combined with image subtraction and crowded-field photometry. This helps us address one of the most controversial topics in current massive star research: the relative importance of binarity in the evolution of massive stars and formation of WRs. Here, we discuss the current state of the field, including how the observed WR populations match with the predictions of both single and binary star evolutionary models. We end with what we believe are the most important next steps in WR research.

**Keywords:** massive stars; Wolf–Rayet stars; local group galaxies; stellar evolution
