In this book invariant probabilities for a large class of discrete-time homogeneous Markov processes known as Feller processes are discussed. These Feller processes appear in the study of iterated function systems with probabilities, convolution operators, certain time series, etc. Rather than dealing with the processes, the transition probabilities and the operators associated with these processes are studied. Special efforts are made to attract newcomers to the theory of Markov processes in general, and to the topics covered, in particular. Most of the results are new and deal with topics of intense research interest.