Undernutrition and starvation remain significant public health issues worldwide, particularly in low- and middle-income countries. This chapter provides a comprehensive exploration of the epidemiology, causes, and consequences of undernutrition and starvation, with a focus on understanding their far-reaching impacts on global populations. The chapter begins by defining undernutrition and starvation, highlighting their public health significance and outlining various anthropometric, biochemical, and clinical measures used to assess these conditions. The global prevalence and regional variations of undernutrition are examined, with a focus on high-risk populations such as children, women, and those affected by pandemics like COVID-19. Socioeconomic, political, environmental, and biological factors contributing to undernutrition are explored, including poverty, food insecurity, conflict, and climate change. A detailed analysis is provided on the immediate and long-term health effects of undernutrition, such as acute malnutrition, impaired immune function, and the development of chronic diseases. Additionally, the chapter outlines the socioeconomic consequences of undernutrition, including its impact on education, productivity, and intergenerational health. Strategies for prevention and intervention are discussed, focusing on policy initiatives, community-based interventions, and the role of international organizations in addressing the crisis. The chapter concludes with insights into future directions, highlighting the need for innovative approaches and continued research to combat undernutrition and starvation effectively. This chapter aims to provide a holistic understanding of these pressing issues, their causes, and potential solutions to mitigate their devastating effects on individuals and societies worldwide.