This chapter explores the theoretical perspectives that underpin modularity methodology in construction, providing a foundation for understanding its conceptual and practical applications. It begins by defining modularity methodology as a systematic approach to designing, manufacturing, and assembling components in a way that enhances efficiency, flexibility, and quality. The chapter highlights the relevance of theoretical perspectives in shaping the adoption and adaptation of modular construction in diverse project contexts. Various approaches to modularity methodology are examined, reflecting how different schools of thought address design principles, process integration, and supply chain coordination. These approaches reveal the multifaceted nature of modularity, where concepts from manufacturing, lean construction, and systems thinking converge to create streamlined and adaptable processes. Furthermore, the discussion includes established modularity methodology models, each providing structured frameworks for planning, execution, and evaluation. These models guide practitioners in aligning design decisions, production strategies, and assembly techniques to achieve desired project outcomes. The chapter highlights how modularity methodology can address important construction challenges like time constraints, quality assurance, cost management, and sustainability goals by integrating these theoretical viewpoints. It also emphasises how crucial it is to modify these frameworks to fit project settings, legal requirements, and stakeholder requirements. In summary, the chapter offers modularity methodology as a flexible, theory-based approach that blends creativity and pragmatism, rather than just as a technical procedure. This theoretical foundation lays the groundwork for future discussions on its useful applications, advantages, and drawbacks in the construction sector and serves as the foundation for well-informed decision-making.