The primary notion of a CTRW is to break a time interval (0,t) into subintervals defined by the instants t1, t2, … tn, at which points in time a system is assumed to be subject to certain fluctuations or collisions that mimic the random events caused by the surrounding heat bath. The underlying stochastic process is then a chain of collisions or an ongoing renewal of a stochastic sequence. The basic idea is illustrated in Figure 7.1.