“Adhesion” is the term used to describe the interaction of electrically neutral solid surfaces, which is usually attractive and decreases rapidly with distance, e.g., due to van-der-Waals forces. This chapter is devoted to (frictionless) normal contact problems with adhesion in the descriptions by Johnson, Kendall and Roberts (JKR), Derjaguin, Muller and Toporov (DMT), as well as Dugdale and Maugis. In addition to the presentation of the contact solution, the focus is on the discussion of the stability of the equilibrium configuration of adhesive contact. Single and periodic contacts are discussed.