Hundreds of mirror segment, thousands of high precision actuators, highly complex mechanical, hydraulic, electrical and other technology subsystems, and extremely sophisticated control systems: an ELT system consists of millions of individual parts and components each of them may fail and lead to a partial or complete system breakdown. Component and system reliability does not only influence the acquisition costs of a product, it also defines the necessary maintenance work and the required logistic support. Taking the long operational life time of an ELT into account, reliability and maintainability are some of the main contributors to the system life cycle costs. Reliability and maintainability are key characteristics of any product and have to be designed into it from the early beginning; they can neither be tested into a product nor introduced by numerous maintenance activities. This presentation explains the interconnections between Reliability, Availability, Maintainability and Safety (RAMS) and outlines the necessary RAMS and Reliability Centered Maintenance (RCM) processes and activities during the entire life cycle of an ELT and an ELT instrument from the initial planning to the eventual disposal phase.