This book offers a novel perspective for conceptualising legality in market exchanges. It challenges the conventional binary of "legal" versus "illegal" markets by introducing the concept of variably legal markets - arenas of exchange where legality is conditional, multidimensional, and context-dependent. Drawing on criminology, law, economics, and regulatory studies, the editors argue that many contemporary markets - such as those involving commercial sex, performance-enhancing drugs, and cryptocurrencies - operate in a blurry middle ground shaped by overlapping legal regimes, inconsistent enforcement, and shifting socio-political norms. To advance this perspective, this collection includes illustrative case studies from experts in this field to reveal how legal status fluctuates across jurisdictions, supply chains, and actors, and how this ambiguity complicates both scholarly analysis and policy interventions. Paoli and Lord call for a more nuanced approach that moves beyond rigid classifications and instead embraces the complexity of real-world market dynamics. This work not only bridges gaps between organised crime and white-collar crime literature but also sets a new agenda for empirical research and regulatory reform. This collection will be essential reading for students and scholars of criminology, economics, and law. It will also be useful for policymakers and practitioners seeking to understand and govern the messy realities of modern markets.