AbstractIn this review, we present a general overview of organic molecules and materials for non‐linear optics, with emphasis on materials for frequency doubling and for the Pockels or electro‐optic effect. After a short introduction on the molecular basis of second‐order non‐linearity, we shall discuss the relevant materials aspects of three important classes of organic non‐linear optical materials: organic crystals, Langmuir‐Blodgett films and poled polymers. The latter class of materials is, in our opinion, the most versatile of these three. We shall present some representative and recent examples of various types of poled polymer materials, their synthesis and their non‐linear optical properties.