With large data sets from the largest telescopes in the world, such as the Very Large Telescope in Chile, I study the effect that the most massive stars we know of have on their environment. These stars, which have masses 8 times and above that of our Sun, shape the material within the regions they form in, they contribute to the formation of new generations of stars, and they regulate the evolution of entire galaxies. By comparing a large number of observations of "feedback in action" to each other and to simulations, it is possible to determine how feedback from massive stars depends on a range of characteristics, such as the location of the stars within the galaxy, the number of massive stars driving the feedback, or even the chemical composition of the star-forming regions