The chapter discusses the health benefits of *Lactobacillus* species and the mechanisms by which they exert these benefits. It highlights the role of *Lactobacillus* in maintaining gut health, including the prevention and treatment of gastrointestinal infections, inflammatory bowel disease, and colorectal cancer. The text also explores the adaptation and probiotic factors that enable *Lactobacillus* to survive and thrive in the host environment, such as stress resistance mechanisms, maintenance of cell envelope integrity, and DNA and protein repair. The chapter delves into the cell surface structures of *Lactobacillus*, including peptidoglycan, teichoic acids, exopolysaccharides, and cell surface proteins, which play crucial roles in adaptation and interaction with host cells. Additionally, it reviews genetic tools used to study *Lactobacillus* and the mechanisms of survival and persistence in the host, emphasizing the importance of stress resistance and the role of specific genes and molecules in these processes. The chapter concludes by summarizing the key findings and their implications for the broader field of probiotic research.The chapter discusses the health benefits of *Lactobacillus* species and the mechanisms by which they exert these benefits. It highlights the role of *Lactobacillus* in maintaining gut health, including the prevention and treatment of gastrointestinal infections, inflammatory bowel disease, and colorectal cancer. The text also explores the adaptation and probiotic factors that enable *Lactobacillus* to survive and thrive in the host environment, such as stress resistance mechanisms, maintenance of cell envelope integrity, and DNA and protein repair. The chapter delves into the cell surface structures of *Lactobacillus*, including peptidoglycan, teichoic acids, exopolysaccharides, and cell surface proteins, which play crucial roles in adaptation and interaction with host cells. Additionally, it reviews genetic tools used to study *Lactobacillus* and the mechanisms of survival and persistence in the host, emphasizing the importance of stress resistance and the role of specific genes and molecules in these processes. The chapter concludes by summarizing the key findings and their implications for the broader field of probiotic research.