We study the effect of a large set of department characteristics on individual publication records. We control for many individual time-varying characteristics, individual fixed-effects and reverse causality. Department characteristics have an explanatory power that can be as high as that of individual characteristics. The departments that generate most externalities are those where academics are homogeneous in terms of publication performance and have diverse research fields, and, to a lesser extent, large departments, with more women, older academics, star academics and foreign co-authors. Department specialisation in a field also favours publication in that field. More students per academic does not penalise publication. At the individual level, women and older academics publish less, while the average publication quality increases with average number of authors per paper, individual field diversity, number of published papers and foreign co-authors.