Tilting theory and cluster combinatorics (Idun Reiten) ---------------------------------------- In the first lecture we discuss basic properties and results from the theory of cluster algebras of Fomin-Zelevinsky. In the second lecture we introduce and discuss cluster categories. In particular we talk about (cluster)-tilting theory and make comparison with ordinary tilting theory. In the third lecture we discuss various properties of the associated cluster-tilted algebras, and compare with tilted algebras. Then we give some applications to cluster algebras in the last lecture.