Papua New Guinea (PNG) is a nation characterized by immense cultural diversity and deeply entrenched customary land systems. Over 90% of its land is under customary tenure, forming the foundation of identity, social organization, and economic livelihood. While this system preserves cultural autonomy and local ownership, it poses challenges for national development and economic planning. This paper explores how customary land management can support sustainable development in PNG. Using secondary literature, policy analysis, and selected case studies from Morobe, East New Britain, and the Highlands, it examines existing legal frameworks, institutional mechanisms, and practical experiences. The study argues that integrating customary land into formal economic systems through strengthened legal frameworks, capacity-building, and inclusive policies can create a path for equitable and sustainable growth.