Once a niche topic garnering only modest assets and a dedicated following, ESG investing has grown significantly, attracting substantial capital and heightened scrutiny. Today, ESG investments are pervasive, involving significant sums and influencing mainstream financial strategies. With this prominence has come greater complexity, oversight, and criticism. This book explores this new phase of ESG investing, offering insights into its theoretical foundations, the methodologies and variations in ESG ratings, and the practical challenges of investing across various asset classes. It includes a discussion of historical arguments for maximizing returns, a review of financial theories and their limitations, the financial instruments available to investors, and presents an economic and financial rationale for ESG investing that extends beyond governmental mandates or activist-driven agendas. A valuable resource for students, academics, investors, and practitioners, ESG Investing provides a comprehensive understanding of the evolving landscape of ESG finance.