Massive stars (OB-type) play an essential role in the Universe. With their feedback of ionizing photons and their stellar mass loss, these stars govern the ecology of their extended neighborhood. Many massive stars pass through Wolf-Rayet (WR) stages in advanced phases of their evolution. These objects cover a wide range of mass, temperature and luminosity. With the advent of new, high-performance, ground-based and space-borne facilities, the multi-wavelength investigation of hot, massive stars has definitely been boosted over last few decades. It is indeed nowadays possible to study these objects over a wide part of the electromagnetic spectrum, all the way from radio waves to gamma-rays. Some of their basic properties like evolution, populations, classification, emission mechanisms etc. alongwith its multiwavelength view will be discussed during this talk.