Extremal (especially BPS) black holes are of special importance in string theory and AdS/CFT. Their near-horizon geometries provide a precise tool for investigating certain aspects of such black holes. I will begin with a discussion of some general properties of near-horizon geometries. I will then describe some specific applications of these ideas which will include: a classification of near-horizon geometries of asymptotically AdS(5) supersymmetric black holes with two rotational symmetries (of relevance to AdS/CFT), a proof of symmetry enhancement of generic near-horizon geometries in D=4,5 (of relevance to the attractor mechanism), near-horizon geometries in D greater than 5 and finally some open problems.