In this paper, we present an overview of some recent progress in inverse problems. We shall discuss several time independent problems. In general we consider a bounded region in ${\mathbb R}^n$, which represents a body, and a partial differential equation, or system of equations, which represents the physics inside the body. The problem is to deduce the interior physical parameters – coefficients of the differential equation – from measurements made at the boundary of the region. We begin with the simplest example.