Availability assessment is of paramount importance to guarantee uninterrupted operation of a variety of commercial-grade information and networked systems. In this paper, we present practical case studies that show how to use stochastic analytic modeling approaches to quantitatively assess the availability of such systems. We present non-state-space models, statespace models and hierarchical models. We describe the details of these modeling approaches to assess system availability. Copyright © 2012 John Wiley & Sons, Ltd.