One of the key pillars in our understanding of the chemical (Matteucci 2012) and dynamical evolution of galaxies is our knowledge about massive stars (Massey 2003), and the O-type stars (M ZAMS ⇠ 15/20 60/80 M ) in particular. Massive stars play a crucial role in shaping their environment due to their thrilling short lives during which they greatly a↵ect their surroundings (through UV radiation and strong stellar winds), and violent deaths (supernova explosions) and even have an important e↵ect in star and planetary formation (Bally et al. 2005). Due to their short lifespan, massive stars are also great tracers of galactic structure because, with the exception of the runaway stars, they
do not shift far away from their birthplace in the stellar formation regions (Ward et al. 2020; Pantaleoni González et al. 2021).
However, any study of massive stars will be incomplete without a thorough understanding of their multiplicity, and the role of that characteristic in their formation, evolution and death (Zinnecker & Yorke 2007; Mason et al. 2009; Sana et al. 2012; Chini et al. 2012; Sana et al. 2013; Sota et al. 2014; Barbá et al. 2017a). Besides, a large fraction of them are short-period systems, which leads to a very high rate of interactions between the members of the system. Sana et al. (2012) proposed that nearly 70% are expected to exchange mass with a companion during their lifetimes, and almost a third will do while both components are still on the main-sequence. Therefore, it is crucial to obtain an accurate knowledge of the orbital and stellar properties in order to understand their role as a population.