In this chapter, we present an overview of the Network Functions Virtualization (NFV) concept and discuss the main design features with respect to their dependability implications. As NFV systems are expected to be used extensively in the future to enable flexible and robust provisioning of numerous network services, including mobile telecommunications, they need to be protected against large-scale failure scenarios. We analyze the dependability of NFV systems from two different perspectives and identify the corresponding challenges together with the selected existing solutions. Finally, we review Cloud application technologies and design models in implementing Virtual Network Functions.