Acid-Fast Bacilli (AFB) are a group of bacteria that resist decolorization by acids during staining procedures. This characteristic is primarily due to their thick, waxy cell walls, which contain mycolic acids. The most well-known AFB is Mycobacterium tuberculosis, the causative agent of tuberculosis. AFB are typically identified using special staining techniques, such as the Ziehl-Neelsen stain. These bacteria are important in clinical microbiology because they can cause serious infections in humans. In addition to tuberculosis, other species like Mycobacterium leprae can lead to leprosy. Detecting AFB in clinical samples is crucial for diagnosing and managing these diseases effectively.