The carrier states are considered in disordered or in not-fully-ordered nometallic systems under conditions when the internal parameters of the medium change relatively rapidly. In a definite region of temperatures and electron-medium interaction constants, there can be produced in these systems fluctuons, i.e., large-radius formations in which the electron is autolocalized near the change of the fluctuation, concentration, or internal parameter of the medium, and maintains the fluctuations stationary through its field. The characteristics of fluctuons are investigated in solutions, in para- and ferromagnetic semiconductors, in systems near the critical point in a solution, or in a gas-liquid system, and also near a first-order phase transition point. The mechanism of fluctuon mobility is discussed. A transition of electrons into fluctuonic states can have the character of a smeared first-order transition and can alter strongly different electronic properties of the system, as well as some other system properties. The possibility of spontaneous dispersion of a system with easily-alterable internal parameters is considered at a relatively high carrier density.