This chapter explores the significance of Online Brand Communities (OBCs) in enhancing consumer engagement and co-creation. Grounded in theories such as Consumer Engagement Theory and User Engagement Theory, it highlights various dimensions of engagement – conative, cognitive, sensorial, behavioural, and co-creative – as observed in activity community eco-systems. Using real-world examples, GoPro, Duolingo and Airbnb, the chapter demonstrates how OBCs enable emotional connection, peer-driven innovation and cost-effective support. It introduces the Community Engagement Influence Framework (CEIF), which explains how content, culture, and feedback triggers generate layered engagement outcomes across individual, community, and brand levels. The rationale for this chapter lies in the increasing relevance of community-centric environments where consumers seek authenticity, peer validation, and opportunities for participation beyond transactional exchanges. By decoding how structured communities foster such engagement, the chapter provides a practical lens for marketers and platform designers to enhance relationship-building. It also reflects on emerging dynamics such as integrating Artificial Intelligence (AI) to personalise experiences and the parallel rise of anti-brand communities as counter-narratives to mainstream building. Designed to inform researchers and practitioners, this work provides insights into participation and value generation in a community-led marketing context. This chapter extends prior engagement frameworks by introducing the Community Engagement Influence Framework (CEIF), which uniquely incorporates sensorial and co-creative dimensions alongside cognitive, conative, and behavioural aspects. Unlike earlier models, CEIF links engagement triggers with measurable brand outcomes such as customer lifetime value (CLV) uplift, engagement index, and Net Promoter Score (NPS). It also anticipates future dynamics by exploring how AI-driven personalization, Web3 community governance, and immersive technologies such as AR/VR are reshaping online brand communities (OBCs) across diverse cultural and ethical contexts.