  These are expanded and revised notes for a minicourse entitled "Affine
W-algebras", which took place as part of the thematic month "Quantum
Symmetries" at the Centre de Recherches Mathematiques in Montreal, Canada in
October 2022. The first few sections consist of rapid introductions to vertex
algebras, affine Kac-Moody algebras and their integrable and admissible
modules, and the homological BRST procedure for quantum Hamiltonian reduction.
The affine W-algebras are defined using these ingredients. The remainder of the
notes treats the structure and representation theory of the exceptional affine
W-algebras, with emphasis on modular tensor categories of representations.
