Women in Science, Technology, Engineering and Mathematics (STEM) fields remain severely underrepresented. For instance, in Spain, women represent about 15% of full (catedras) professorships. Moreover, women are judged to be less competent, receive less payment and research facilities, and are less likely to be awarded research grants compared with male scientists. The different mechanisms leading to this disparity have been investigated and more is brought to light by ongoing research. In this talk we will explain the different challenges faced by women in STEM careers, the reasons and the mechanisms through which they emerge, and changes (big and small) that we can all do to improve the current dire scenario. We will also show how gender, race, class, and sexual identity discriminations are entangled and contribute to leaving out minorities from academia.