Here we shall study turbulence evolution both close to the stationary cascade solutions obtained in Chap. 3 and far from them. Section 4.1 deals with the behavior of distributions slightly different from the Kolmogorov–Zakharov (KZ) solutions. The difference may be either a small variation in the boundary conditions (source and sink) or a direct perturbation of the occupation numbers in the inertial interval. Small perturbations are studied in terms of linear stability theory, where the main object is the kinetic equation linearized with respect to the deviation of \(n_k\) from the stationary spectrum. In Sect. 4.1, we describe the basic properties of the linearized collision integral and its neutrally stable modes, i.e., small steady modulations of the cascade distributions. Section 4.2 is the most mathematical one; it presents a linear stability theory for steady solutions of kinetic equations, formulates the stability criterion, and gives examples of instabilities. The final section of this chapter discusses the evolution of nonstationary distributions, which are far from the KZ spectra.