Introduction to the method of multiple scales

Earlier versions of these lecture notes have been used at the Cork Summerschool on Theory and Mathematics Modelling of Ultrashort Pulse Propagation (2013), and as a part of a graduate course in the theory of nonlinear waves in the period 2014-2016. This version has an improved typography and numerous typoes has been corrected. It also has been extended with a section where the method of multiple scales is applied to boundary layer problems for ODEs. The document consists of 78 pages and contains 9 figures.