Bloodletting is an ancient medical practice that involves the withdrawal of blood from a patient to treat various ailments. It was based on the belief that many diseases were caused by an imbalance of bodily fluids, known as humors. Practitioners used tools like leeches or lancets to draw blood, thinking it would restore health. This practice was common from antiquity through the 19th century, often associated with famous figures like Hippocrates and Galen. However, as medical knowledge advanced, bloodletting fell out of favor, and it is now considered harmful rather than beneficial in most cases.