This careful and accessible text focuses on the relationship between two interrelated subjects in analysis: analytic semigroups and initial boundary value problems. This semigroup approach can be traced back to the pioneering work of Fujita and Kato on the Navier-Stokes equation. The author studies nonhomogeneous boundary value problems for second-order elliptic differential operators, in the framework of Sobolev spaces of Lp style, which include as particular cases the Dirichlet and Neumann problems, and proves that these boundary value problems provide an example of analytic semigroups in Lp.