Schubert varieties and degeneracy loci have a long history in
mathematics, starting from questions about loci of matrices with given
ranks. These notes, from a summer school in Thurnau, aim to give an
introduction to these topics, and to describe recent progress on these
problems. There are interesting interactions with the algebra of
symmetric functions and combinatorics, as well as the geometry of flag
manifolds and intersection theory and algebraic geometry.