On the Singular Locus of a Schubert Variety

Over the past three decades much progress has been made in the area of singularities of Schubert varieties. Because of the rich geometry and combinatorics of the generalized flag variety, all the known results on the singularities of Schubert varieties in the literature involve many different areas of mathematics including geometry, combinatorics and representation theory. In this survey article, we have put together all of the known results on singular loci of Schubert varieties so that this survey could be used as a handbook by both geometers and combinatorialists.