Over the past decade systems engineers have focused on developing methods to address operational uncertainty, reduce complexity, and enhance effectiveness within the system design process. One prevailing concept to address these needs is that of system “ilities;” system-level properties used to describe a system’s ability to cope with change. While the concept of system “ilities” has a fair consensus across the system engineering community, clear definitions and measures for describing system “ilities” are far less common. Today engineers have identified over 80 “ilities” – some of the most common being flexibility and adaptability, but have provided no clear means to distinguish between newer system “ilities” and more traditional properties such as reliability, maintainability and availability. To address this issue; the author proposes the use of a value-centric framework as the foundation for a common lexicon regarding system “ilities.” Using industry definitions, common practices, and exemplars, the author will introduce this value-centric framework and discuss how system “ilities” are derived within this framework. First the author will discuss a three element changeability framework – consisting of Agents, Mechanisms, and Effects – first introduced by Ross. Within this framework Agents represent the change instigators. If a system is changed by an external agent, the system is said to be “flexible.” “Adaptable” systems are then those systems within internal change agents. Mechanisms describe means (e.g. system design choices) to how a system may change from one state to another. A system design choices could include: do nothing (Robustness), increase / decrease a performance parameter (Scalability), or add / subtract new performance parameters (Modifiability). Lastly, Effects represent the resulting change in system value-delivery between states. An epoch construct is introduced as a means to examine system value-delivery across both static & dynamic timescales. For example, on the one hand system design strategies to ensure value delivery within a fixed epoch could include availability, reliability, and maintainability. On the other hand system design strategies to ensure value delivery across varying epochs could include endurability, survivability, modularity, and evolvability. Lastly, system design strategies (consisting of Agents, Mechanisms, and Effects) are constrained by available resources. Addressing changes to these resources within the system design process yield design strategies such as affordability (funding) and sustainability (man-power). A unified system â€œilityâ€ framework provides system engineers new insights into the ability / inability of system concepts to adapt and respond to future uncertainties; assisting in acquisition strategy formulation, providing better understanding of system capabilities leading into the requirements process, and enhancing overall system effectiveness across changing operational environments.