Spectroscopy is a powerful tool to unravel the nature of stellar bodies. For instance, spectra can be used to derive the temperature, gravity, and chemical composition at the surface of a star. If the star is part of a binary system and/or pulsating, spectra can even tell us something about its fundamental parameters mass and radius. In this talk, I will illustrate the opportunities and difficulties related to studying the spectra of pulsating stars or stars in binary systems, with special focus on massive stars of spectral type B.