The world’s busiest landfills represent the scale of modern waste management challenges and the opportunities for transforming waste into energy. Sites such as Puente Hills in the United States, Bordo Poniente in Mexico, Apex Regional in Nevada (USA), Ghazipur in India, and Jardim Gramacho in Brazil highlight diverse approaches to handling millions of tons of municipal solid waste. While developed countries have implemented advanced engineering solutions, including composite liners, leachate treatment, and methane recovery systems, developing nations often struggle with uncontrolled waste growth, environmental pollution, and safety risks. Puente Hills, once the largest landfill in the U.S., pioneered landfill gas-to-energy (LFGTE) systems capable of generating up to 50 megawatts of electricity. Apex Regional continues this trend, capturing methane and refining it into renewable natural gas, turning a disposal challenge into a revenue-generating energy source. Bordo Poniente and Jardim Gramacho illustrate the potential for post-closure methane recovery projects that provide renewable electricity while mitigating greenhouse gas emissions. Conversely, Ghazipur exemplifies the dangers of unmanaged landfills, with towering waste piles leading to environmental crises and safety hazards, despite ongoing efforts to divert waste into waste-to-energy plants. Together, these landfills underscore the dual role of modern waste facilities: essential repositories for urban refuse and emerging contributors to renewable energy strategies. The contrast between advanced sites and struggling megacity landfills highlights the importance of technology, policy, and investment in shaping future waste management. As global waste generation continues to rise, the experience of the world’s busiest landfills demonstrates the need for innovative solutions that balance disposal, energy recovery, and environmental protection.