Bacterial chondronecrosis with osteomyelitis (BCO) is widely recognized as one of the most common causes of lameness in broilers. This chapter starts by summarizing the pathogenesis of BCO. Experimental models that successfully trigger BCO are then reviewed. Sources of bacteria that infect the bones are discussed, with the primary emphasis on bacterial translocation across the gastrointestinal epithelium. Finally, we review the efficacy of probiotics as a prophylactic treatment for BCO.