Gastric cancer (GC) is a significant global health issue, with a strong association between its development and the gastric microbiota. While *Helicobacter pylori* is widely recognized as a key carcinogen, recent studies have highlighted the crucial role of other gastric microbes in the carcinogenic process. Dysregulation of the gastric microbiota can occur throughout the carcinogenic journey, from the development of precancerous lesions to advanced malignancy. This review summarizes the current understanding of the gastric microbiota in GC development and explores its potential clinical implications in diagnosis, prognosis, and therapy. Key findings include: - **Dysbiosis in GC**: The gastric microbiota undergoes significant changes during GC progression, with a decrease in microbial diversity and richness. - **Pathogenic Microbes**: Enriched bacteria such as *Streptococcus* and *Fusobacterium* are associated with GC, contributing to inflammation and carcinogenesis. - **Beneficial Microbes**: Probiotic bacteria like *Bifidobacterium* and *Lactobacillus* show anti-tumourigenic effects, potentially through mechanisms involving short-chain fatty acids and immune modulation. - **H. pylori and Microbiota Interactions**: *H. pylori* infection significantly alters the gastric microbiota, and its eradication can restore microbial diversity, though not always completely. - **Clinical Implications**: Microbial biomarkers show promise in GC diagnosis and prognosis, with diagnostic panels achieving high accuracy. Probiotics may also enhance treatment outcomes by modulating the immune response and reducing *H. pylori* burden. - **Future Directions**: Further research is needed to understand the complex interactions between gastric microbes and GC, including the role of viruses and fungi, and to develop standardized methodologies for microbial analysis. The review emphasizes the potential of modulating the gastric microbiota as a novel and promising approach to prevent and manage GC, highlighting the need for future investigations to translate these findings into clinical practice.Gastric cancer (GC) is a significant global health issue, with a strong association between its development and the gastric microbiota. While *Helicobacter pylori* is widely recognized as a key carcinogen, recent studies have highlighted the crucial role of other gastric microbes in the carcinogenic process. Dysregulation of the gastric microbiota can occur throughout the carcinogenic journey, from the development of precancerous lesions to advanced malignancy. This review summarizes the current understanding of the gastric microbiota in GC development and explores its potential clinical implications in diagnosis, prognosis, and therapy. Key findings include: - **Dysbiosis in GC**: The gastric microbiota undergoes significant changes during GC progression, with a decrease in microbial diversity and richness. - **Pathogenic Microbes**: Enriched bacteria such as *Streptococcus* and *Fusobacterium* are associated with GC, contributing to inflammation and carcinogenesis. - **Beneficial Microbes**: Probiotic bacteria like *Bifidobacterium* and *Lactobacillus* show anti-tumourigenic effects, potentially through mechanisms involving short-chain fatty acids and immune modulation. - **H. pylori and Microbiota Interactions**: *H. pylori* infection significantly alters the gastric microbiota, and its eradication can restore microbial diversity, though not always completely. - **Clinical Implications**: Microbial biomarkers show promise in GC diagnosis and prognosis, with diagnostic panels achieving high accuracy. Probiotics may also enhance treatment outcomes by modulating the immune response and reducing *H. pylori* burden. - **Future Directions**: Further research is needed to understand the complex interactions between gastric microbes and GC, including the role of viruses and fungi, and to develop standardized methodologies for microbial analysis. The review emphasizes the potential of modulating the gastric microbiota as a novel and promising approach to prevent and manage GC, highlighting the need for future investigations to translate these findings into clinical practice.