C*-algebras were first considered in quantum mechanics to model algebras of physical observables. In mathematics, they since then became ubiquitous tools in index theory, the theory of representations of locally compact groups and Alain Connes non-commutative geometry, just to name a few. They are also fundamental in coarse geometry, a subject that has been recently found to be relevant in the theory of topological phases, to circle back to physics.

The lecture will start with a basic introduction to the C*-algebras, discussing in particular the result of Gelfand-Naimark that commutative C*-algebras are isomorphic to continuous functions on a locally compact Hausdorff space, while general C*-algebras can be realized as subalgebras of B(H) for some Hilbert space H.

The lecture will continue with an introduction to K-theory, a tool that has revolutionized the study of C*-algebras in the last decades. Roughly speaking, the idea of K-theory is to understand an algebra by studying the category of modules over it. However, for C*-algebras, K-theory has this additional feature of Bott periodicity, which makes the theory particularly well-behaved.

**Literature**

[B1] B. Blackadar. K-Theory for Operator Algebras.

[B2] B. Blackadar. Operator Algebras.

[RLL] M. Rørdam, F. Larsen, N.J. Laustsen. An Introduction to K-Theory for C*-Algebras.

[WE] N.E. Wegge-Olsen. K-Theory and C*-Algebras. A Friendly Approach.