Massive stars drive the dynamical and chemical evolution of their host galaxy. Mapped across large portions of galaxies, they provide a precise time- and spatial- tomography of the young stellar populations, because they evolve on fast time-scales. Massive stars are very luminous, and dominate the light of distant star-burst galaxies. Studies of stellar populations in local galaxies, spanning a variety of environments and conditions, allow us to understand the star-formation process, and the co-evolution of massive stars and dust. Results from such studies inform stellar and galaxy evolution models, which underpin our interpretation of the integrated light from galaxies in the distant, younger universe. The identification and characterisation of hot (young) massive stars, and of the evolved descendants of intermediate-mass stars, the hot white dwarfs, requires UV data. GALEX has performed the first comprehensive sky surveys in far-UV and near-UV broad bands, providing unprecedented wide-field, sensitive views of young stellar populations in nearby extended galaxies, as well as a census of Milky Way hot stars, and of star-forming galaxies and QSOs at redshifts up to about 2. Hubble’s resolution has enabled multi-band measurements of the resolved stellar constituents of nearby star-forming regions : the spatial structuring of resolved young populations reveals how gas and dust condense to form stars, and how local starbursts evolve and dissolve with time. I will describe our contribution to this topic, and show results from the GALEX surveys, and from HST’s PHAT and TrImS surveys.