This research explores the implementation of social sustainability in area development projects, focusing on the relations between private developers, municipalities, and housing associations in the Netherlands. Although increasingly recognised as a key pillar of sustainable development, social sustainability remains underdeveloped in practice. In particular, the operationalisation of well-being, liveability, and social equity & justice remains challenging. Advancing these aspects is essential for guiding development strategies that respond to pressing urban challenges such as housing shortages and spatial and economic inequality. Yet, a knowledge gap remains in how key actors interpret and operationalise these concepts within development processes. This research addressed that gap by examining actor relations and their influence on the translation of social sustainability goals during planning and implementation. The main research question: “How is social sustainability understood and implemented by private developers, housing associations, and municipalities in area development projects in the Netherlands?” will be addressed using a qualitative approach, combining a literature review, interviews, document analysis, based on three case studies. The research shows that social sustainability is not limited from lack of ambition, but from fragmented timelines, fixed roles, and unaligned interpretations. Integrated outcomes only emerge when actors collaborate early, share responsibility, and move beyond institutional roles toward adaptive, long-term engagement throughout the development process. Moving forward, more attention is needed for building shared understandings early in the process, rethinking financial and organisational models, and embracing the complexity of social systems alongside the built environment.