Human urine has long been valued for its nutrient content, containing essential elements like nitrogen, phosphorus, and potassium that support plant growth. Ancient civilizations such as those in Greece, China, and Rome used urine, along with feces, as natural fertilizers for crops. However, the rise of synthetic fertilizers in the 20th century led to a decline in the use of human waste as a resource. Today, about half the world's population relies on food grown with synthetic fertilizers. However, recent increases in the cost of synthetic fertilizers, particularly due to the Iran war, may encourage a return to using urine as a fertilizer, a practice sometimes called "peecycling." Before modern sanitation systems, human waste was stored in cesspits or collected by workers who transported it to farms for use as fertilizer. The development of centralized sewage systems in the 19th century improved public health by reducing the spread of diseases but also changed the perception of human waste from a valuable resource to something considered waste. This shift contributed to the decline of traditional practices that repurposed human excreta for agricultural use. In the 19th century, countries competed for access to guano, a natural fertilizer made from seabird droppings, but this resource was limited. This led to the creation of synthetic fertilizers in the early 20th century, which dramatically increased crop yields. However, the production of synthetic fertilizers comes with environmental and social costs. The process to create synthetic nitrogen fertilizers, known as the Haber-Bosch process, is energy-intensive and relies on natural gas. Phosphorus fertilizers, on the other hand, are derived from phosphate rock, a finite resource mostly mined in Western Sahara, a region disputed between Morocco and other nations. Countries with poor soil quality, such as Australia, heavily depend on imported synthetic fertilizers. Australia imports 3.5 to 4 million metric tons of synthetic fertilizers each year, making it vulnerable to global market fluctuations and geopolitical tensions. In contrast, urine is a local, sustainable source of nutrients. It contains nearly all the nitrogen and about half the phosphorus found in wastewater, but these nutrients become harder to access once mixed with other waste. Separating urine from wastewater can reduce greenhouse gas emissions from treatment plants and offer a more sustainable alternative. Urine-based fertilizers are being explored in various parts of the world. In the United States, the Rich Earth Institute has promoted community-based urine recycling programs for over a decade. In Europe, a Swiss startup called VunaNexus is using diverted urine to create sustainable fertilizers. Some sports stadiums in the UK, Sweden, and South Africa are testing the use of urine-based fertilizers, while researchers in Australia are experimenting with it in urban parks. Despite these efforts, the practice still faces challenges, including concerns about pathogens, pharmaceutical residues, and inconsistent plumbing regulations. Public perception also remains a barrier, but ongoing efforts aim to change this view and promote the benefits of urine recycling as a viable, eco-friendly alternative.