  We review the theory of regenerative processes, which are processes that can
be intuitively seen as comprising of i.i.d.\ cycles. Although we focus on the
classical definition, we present a more general definition that allows for some
form of dependence between two adjacent cycles, and mention two further
extensions of the second definition. We mention the connection of regenerative
processes to the single-server queue, to multi-server queues and more generally
to Harris ergodic Markov chains and processes. In the main theorem, we pay some
attention to the conditions under which a limiting distribution exists and
provide references that should serve as a starting point for the interested
reader.
