Enterprise Architecture (EA) and IT Infrastructure have emerged as foundational pillars in aligning IT strategies with business objectives, fostering operational excellence, and ensuring competitive advantage. This chapter explores the theoretical underpinnings, models, and frameworks that have shaped the domain, including The Open Group Architecture Framework (TOGAF), Information Technology Infrastructure Library (ITIL), and the Strategic Alignment Model. Furthermore, it delves into the evolution of these frameworks in addressing contemporary challenges, such as cloud computing, DevOps, and sustainability.