The continuous time random walk (CTRW) framework (Montroll and Weiss 1965, Montroll and Scher 1973) was described in our earlier Chapters 6 through 9. The CTRW scheme is conceptually appealing and at the same time mathematically flexible to facilitate incorporation of various generalizations. Thus, although CTRW is usually set in the context of a Poisson processdriven pulse sequence leading to stationary Markov systems, incorporation of non-Poissonian pulsing with concomitant waiting-time distributions was seen in Chapter 7 to yield anomalous diffusion.