This chapter explores cross-border air pollution as a serious challenge that affects both the environment and human health. It looks at how different regions, such as Europe, Southeast Asia, North America, and East Asia, have built legal and institutional systems to deal with pollution that crosses national borders. Using a doctrinal and comparative method, it examines key agreements, policy tools, and the role of regional cooperation. The chapter also discusses how uneven capacity and lack of enforcement affect outcomes. It highlights the need for stronger legal frameworks and inclusive cooperation to protect air quality, support public health, and promote sustainable development across regions.