The evolution of systems in random media is a broad and fruitful field
for the applica- tions of different mathematical methods and theories.
This evolution can be character- ized by a semigroup property. In the
abstract form, this property is given by a semigroup of operators in a
normed vector (Banach) space. In the practically boundless variety of
mathematical models of the evolutionary systems, we have chosen the
semi-Markov ran- dom evolutions as an object of our consideration. The
definition of the evolutions of this type is based on rather simple
initial assumptions. The random medium is described by the Markov
renewal processes or by the semi- Markov processes. The local
characteristics of the system depend on the state of the ran- dom
medium. At the same time, the evolution of the system does not affect
the medium. Hence, the semi-Markov random evolutions are described by
two processes, namely, by the switching Markov renewal process, which
describes the changes of the state of the external random medium, and by
the switched process, i.e., by the semigroup of oper- ators describing
the evolution of the system in the semi-Markov random medium.