Coherence is a highly valued notion in law and it is especially sought after in investor-state dispute settlement. At the same time, coherence is a largely underexplored concept in international law literature. The introductory chapter serves to set the stage for the book’s investigation. To that end, the chapter outlines: (i) the impetus behind the choice of coherence as a subject for inquiry; (ii) the principal, so-called ‘bottom-up’ perspective from which the subject of coherence is examined in the book; and (iii) the core thesis advanced in relation to the dual, substantive and methodological, nature of coherence and its role in judicial reasoning in investor-state dispute settlement.