Émilie du Châtelet (1706-1749) played a remarkable role in the development of early modern physics. In her monograph "Institutions de Physique" (Foundations of Physics) she integrated the work of Galileo, Huygens, Leibniz and Newton into a coherent body of ideas. She translated Newton’s "Principia" into French, adding some 300 pages of comments and additional material; in particular, collaborating with Clairaut she was among the first physicists to rework Newton’s theories into the modern language of Leibnizian calculus. In this talk I will focus on the "Institutions" and highlight among other things her defense of the importance of the concept of mechanical energy in analyzing physical processes.