This text concerns ‘semiclassical’ within various meanings. These include the familiar JWKB approximation and its phase-integral generalizations in Chapter 2 to two and four transition points with or without one or two poles: by corollary, crossing and non-crossing nonadiabatic collision theory. Above and below threshold Wannier ionization is covered in Chapter 3 where the large parameters are the inverses of the variation of the hyperspherical angles from their ridge values. The more familiar impact parameter treatment, in which the possibly relativistic heavy-particle relative motion is treated classically and the electrons quantally, is well covered in Chapter 4. Diffusion in solids and liquids is described in Chapter 5 where typically the large parameter is the height of the barrier which is overcome by thermal agitation. Hypergeometric functions are introduced in Chapter 1 and Mittag-Leffler functions in Appendix B.