In order to understand how protection, fault passage indicators and control systems apply to distribution networks, this chapter examines the mechanism of faults. In the most fundamental terms, the majority of faults on a power system are caused by a partial or complete failure of electrical insulation, which leads to an increase in the current. The type of fault can also be categorized into three supplementary categories: self-clearing, transient and permanent. The way in which faults affect a distribution system depends on the type of fault and the protection that is available, which in turn depends on the type of distribution system. Quantifying the reliability of distribution networks has now evolved into a set of defined reliability indices that are recognized throughout the industry. The chapter focuses on the commonly accepted indices as defined by the IEEE and discusses how they are applied to assess and compares the performance of different distribution networks and automation strategies.