The issue of non-performing loans (NPLs) remains a persistent challenge for both developed and emerging economies around the world. The jurisdictions have adopted a wide array of regulatory, policy, and supervisory measures to combat this problem. While some of these initiatives have met with success, others have fallen short of achieving the intended outcomes. This chapter critically examines the evolution and global proliferation of the NPL problem by reviewing existing literature, identifying key gaps in the research, and offering insights into why certain strategies have struggled. Based on this review, the chapter formulates essential research questions that will guide the subsequent analysis and lays out the research methodology used to answer these questions. A central part of the discussion focuses on the diverse definitions of NPLs employed across different jurisdictions, and it advocates for a harmonized approach to NPL assessment. Such an approach, the chapter argues, would provide clearer benefits to policymakers and regulators when tackling NPL issues. Additionally, the chapter categorises selected jurisdictions based on the severity of their NPL challenges, which leads to the selection of three specific jurisdictions for in-depth case studies. By presenting a comprehensive overview of the current challenges surrounding NPLs, the research methodology, the debate over definitions, and the classification of jurisdictions, this chapter sets the foundation for the subsequent exploration of regulatory, policy, and supervisory responses to NPLs. These responses, spanning from the Global Financial Crisis (GFC) to the COVID-19 pandemic, will be discussed in detail in the following chapters.