Millions of people around the world live in and travel through the shadows. Compelled to leave home, they migrate irregularly without proper documentation to gain access to jobs, education, healthcare, food, and other essential services. Irregular migration exists because there are not enough opportunities for safety and prosperity at home and too few conventional means through which to remedy that lack of opportunity. Recognizing the critical, understudied, and often misunderstood nature of this global phenomenon, the CSIS Project on Prosperity and Development produced a research study on irregular migration involving field research in Mexico, Eritrea, and Ghana. This report, which builds on CSIS's past work on the global forced migration crisis, aims to shine a light on irregular migration and contribute to an enormously consequential conversation.