Chapter 2 describes Lorentz’s appointment as university professor, his move from Arnhem to Leiden, the methodology and views on physics in his inaugural lecture on molecular theories in physics, and his use of mathematics for the development of his theoretical work on optics and molecular theory, among other topics. Lorentz’s induction and involvement in the Royal Academy of Sciences is discussed in this chapter. Other sections are devoted to Lorentz’s experimental work in physics together with Pieter Zeeman, and to his work with various friends and colleagues, like Kamerlingh Onnes and Van de Sande Bakhuyzen. Lorentz’s first foreign contacts are explored, in particular those with Woldemar Voigt, Ludwig Boltzmann, Felix Klein, and Walther Nernst. Lorentz’s teaching and his first public activities are discussed here, as well as his marriage and his family life.