This chapter explores the prehistoric and early historic period of the Indonesian archipelago. It analyzes archaeological and anthropological evidence to trace the development of early agrarian societies, inter-island trade, and the beginnings of social stratification. The migration of Austronesian-speaking peoples and the diffusion of wet-rice agriculture are discussed as key transformative forces. The chapter highlights how geography shaped settlement patterns, ecological adaptation, and economic differentiation. It argues that the foundations for Indonesia’s later complexity—both politically and economically—were laid in this formative period, with early networks of exchange sowing the seeds for state formation and cultural convergence.