Colloquium : Disclination loops, point defects, and all that in nematic liquid crystals

Topological defects play a strong role in the physics of a large class of systems with interacting components such as in the case of nematic liquid crystals. Recent experimental progress in this area has attracted a lot of attention. In this Colloquium the experimental situation is reviewed and the theoretical approaches that can describe the rich phase diagram of these systems are discussed.