This chapter deals with the mechanical behaviour of a single laminate layer and presents Hooke’s generalised law for a variety of different material symmetries. It is presented in terms of stiffnesses and compliances as well as in terms of the so-called engineering constants. The elementary transformation rules for stiffnesses and compliances, which are essential for the treatment of layered anisotropic structures, are discussed as well as the transition to the plane case, which is relevant for many engineering applications. The chapter concludes with a brief overview of the determination of effective properties of anisotropic single layers using so-called rules of mixture.