The gut microbiota plays a crucial role in maintaining human health and is implicated in a wide range of diseases. This chapter begins by providing an overview of the gut microbiota, highlighting its diverse microbial communities and their essential functions in digestion, immune regulation, and homeostasis. The interplay between gut microbiota and neurodegenerative diseases (NDs) is explored, with a focus on Parkinson’s disease (PD) and Alzheimer’s disease (AD), underscoring how microbial imbalances may contribute to the pathogenesis of these disorders. Next, the relationship between gut microbiota and cardiovascular diseases (CVDs), including hypertension and atherosclerosis (AS), is discussed, demonstrating how microbial metabolites affect cardiovascular health. The chapter also examines the role of gut microbiota in metabolic diseases, such as obesity, diabetes, and nonalcoholic fatty liver disease (NAFLD), detailing how dysbiosis influences metabolic pathways. Furthermore, the gut microbiota’s involvement in gastrointestinal (GI) diseases, including inflammatory bowel disease (IBD) and colorectal cancer (CRC), is reviewed. The chapter concludes by discussing future research directions and potential therapeutic strategies targeting the gut microbiota to improve disease outcomes.