Mitotic homologous recombination (HR) is essential for maintaining genomic stability and preventing tumorigenesis by precisely repairing DNA double-strand breaks (DSBs) and other lesions. HR is a key repair pathway during the S and G2 phases of the cell cycle, using the sister chromatid as a template. Deficiencies in HR lead to error-prone repair pathways such as non-homologous end joining (NHEJ) and single-strand annealing (SSA), contributing to genome instability. Key HR proteins, including BRCA1 and BRCA2, suppress genome instability and act as tumor suppressors. Mutations in these proteins are associated with developmental abnormalities and cancer. HR involves DNA strand exchange, a process facilitated by RAD51, which forms nucleoprotein filaments to promote repair. End resection generates 3' single-stranded tails, which are essential for HR. RAD51 filaments are formed with the help of accessory factors, and strand invasion leads to repair synthesis using the donor duplex as a template. HR can result in non-crossovers or crossovers, with non-crossovers being more common in mitotic HR. Crossovers are important in meiosis but less so in mitosis. HR is distinct from NHEJ and SSA, with HR being more accurate and less error-prone. HR is restricted to S and G2 phases due to the availability of sister chromatids and regulatory mechanisms. HR is crucial for repairing DSBs encountered during DNA replication, while NHEJ is active throughout the cell cycle. SSA is a RAD51-independent pathway that requires resected ends and is inhibited by NHEJ components. HR plays a critical role in tumor suppression, with BRCA1 and BRCA2 being key tumor suppressor genes. Mutations in these genes lead to genomic instability and cancer predisposition. PALB2, a BRCA2-interacting protein, is also involved in HR and tumor suppression. BRIP1, a DNA helicase, is essential for HR and is associated with Fanconi anaemia. BRCA1 and BRCA2 interact through PALB2, and their dysfunction leads to HR defects and cancer. HR is tightly regulated by cell cycle phase coordination, post-translational modifications, and accessory factors. BRCA1 and BRCA2 are central to HR, while other proteins like BRIP1 and PALB2 have more peripheral roles. Mutations in HR-related genes, such as BRCA1, BRCA2, and PALB2, increase cancer risk, particularly in breast and ovarian cancers. Despite their importance, the exact mechanisms of HR and its regulation remain areas of active research. Defective HR is a target for emerging cancer therapies, highlighting its significance in maintaining genomic stability and preventing tumorigenesis.Mitotic homologous recombination (HR) is essential for maintaining genomic stability and preventing tumorigenesis by precisely repairing DNA double-strand breaks (DSBs) and other lesions. HR is a key repair pathway during the S and G2 phases of the cell cycle, using the sister chromatid as a template. Deficiencies in HR lead to error-prone repair pathways such as non-homologous end joining (NHEJ) and single-strand annealing (SSA), contributing to genome instability. Key HR proteins, including BRCA1 and BRCA2, suppress genome instability and act as tumor suppressors. Mutations in these proteins are associated with developmental abnormalities and cancer. HR involves DNA strand exchange, a process facilitated by RAD51, which forms nucleoprotein filaments to promote repair. End resection generates 3' single-stranded tails, which are essential for HR. RAD51 filaments are formed with the help of accessory factors, and strand invasion leads to repair synthesis using the donor duplex as a template. HR can result in non-crossovers or crossovers, with non-crossovers being more common in mitotic HR. Crossovers are important in meiosis but less so in mitosis. HR is distinct from NHEJ and SSA, with HR being more accurate and less error-prone. HR is restricted to S and G2 phases due to the availability of sister chromatids and regulatory mechanisms. HR is crucial for repairing DSBs encountered during DNA replication, while NHEJ is active throughout the cell cycle. SSA is a RAD51-independent pathway that requires resected ends and is inhibited by NHEJ components. HR plays a critical role in tumor suppression, with BRCA1 and BRCA2 being key tumor suppressor genes. Mutations in these genes lead to genomic instability and cancer predisposition. PALB2, a BRCA2-interacting protein, is also involved in HR and tumor suppression. BRIP1, a DNA helicase, is essential for HR and is associated with Fanconi anaemia. BRCA1 and BRCA2 interact through PALB2, and their dysfunction leads to HR defects and cancer. HR is tightly regulated by cell cycle phase coordination, post-translational modifications, and accessory factors. BRCA1 and BRCA2 are central to HR, while other proteins like BRIP1 and PALB2 have more peripheral roles. Mutations in HR-related genes, such as BRCA1, BRCA2, and PALB2, increase cancer risk, particularly in breast and ovarian cancers. Despite their importance, the exact mechanisms of HR and its regulation remain areas of active research. Defective HR is a target for emerging cancer therapies, highlighting its significance in maintaining genomic stability and preventing tumorigenesis.