This text represents an account of ergodicity and the stability of random processes. It explores the important processes of Markov chains (MC) in arbitrary state space, stochastic recursive sequences (SRC), and Markov chains in random environments (MCRI), as well as their continuous time analogues. Special attention is also paid to vector-valued processes and their application to establish conditions of ergodicity in queueing and communication networks like polling networks, Jackson networks and the multi-access networks associated with the ALOHA algorithm.