This chapter analyzes the structural transformation of modern investing driven by the rise of indices and exchange-traded funds (ETFs). It explores how indices translate complex market data into systematic benchmarks that underpin portfolio construction and asset pricing, while ETFs operationalize these frameworks by providing liquid, transparent, and cost-efficient access to diversified exposures. The discussion emphasizes the intellectual shift from active selection toward passive, factor-based investing, and examines how the widespread adoption of index-linked instruments has reshaped market efficiency, capital allocation, and investor behavior, reflecting a fundamental redefinition of the global investment paradigm.