This book reviews the first set of investment arbitration awards rendered under a new generation of investment treaties that actively balances investment protection and host state flexibility and finds that state-driven reform is being rolled back through an arbitral backlash as new investment agreements reproduce old interpretive outcomes. Combining robust empirical and computational analysis, new comprehensive datasets on investment treaties and awards, and a range of theories from law and economics to complexity science, this book proceeds in three steps. First, it traces state-driven reforms of investment treaty design over seven decades. Second, it demonstrates that these reforms are undermined in practice as tribunals rely on most-favored-nation treatment clauses, customary international law, and precedent to interpret new treaties like old ones. Third, the book suggests how states can preserve and amplify the impact of state-driven reforms by leveraging forward-looking interpretation, data-driven renegotiation, and tax-style multilateralization to modernize old treaties in light of new ones.