Wolf-Rayet stars (WRs) are the penultimate evolutionary stage for stars more massive than 25-40 Msun, and are considered immediate progenitors of stellar mass black holes. The formation of WRs through single or binary stellar evolution channel is a debated topic, and the contribution of the two channels is uncertain. To get more insights into this, spectroscopic studies have attempted to determine the multiplicity of WRs, but are largely limited to relatively high mass ratios and short periods. In this talk, I will discuss a complementary approach to this problem with infrared interferometry and highlight the key discoveries and limitations of this method.