Massive stars play a ubiquitious and significant role in the evolution of our Universe, and can be regarded as true “cosmic engines”. In this talk, I will give an overview about specific aspects, namely line-driven winds (part 1) and quantitative spectroscopy (part 2) of hot massive stars, astrophysical fields that were in the focus of my scientific work during the last 40 years. Emphasis will be given on wind inhomogeneities that need to be considered in the modeling of massive star atmospheres, to infer correct wind (but also stellar) parameters when comparing observed with synthetic spectra.