The relationship between cancer and microbes is complex, with microbes potentially increasing, diminishing, or having no effect on cancer susceptibility. This review explores how microbes and the microbiota can amplify or mitigate carcinogenesis, responsiveness to cancer therapeutics, and cancer-associated complications. Microbes can influence carcinogenesis by altering host cell proliferation and death, guiding immune system function, and affecting metabolism of host-produced factors, ingested foodstuffs, and pharmaceuticals. The review highlights the roles of specific microbes and the microbiota in cancer development, progression, and treatment, emphasizing the need for a multidisciplinary approach to understanding and exploiting these interactions. It also discusses the potential of microbial-based therapeutics and the importance of studying the microbiome in cancer diagnosis, prognosis, and treatment.The relationship between cancer and microbes is complex, with microbes potentially increasing, diminishing, or having no effect on cancer susceptibility. This review explores how microbes and the microbiota can amplify or mitigate carcinogenesis, responsiveness to cancer therapeutics, and cancer-associated complications. Microbes can influence carcinogenesis by altering host cell proliferation and death, guiding immune system function, and affecting metabolism of host-produced factors, ingested foodstuffs, and pharmaceuticals. The review highlights the roles of specific microbes and the microbiota in cancer development, progression, and treatment, emphasizing the need for a multidisciplinary approach to understanding and exploiting these interactions. It also discusses the potential of microbial-based therapeutics and the importance of studying the microbiome in cancer diagnosis, prognosis, and treatment.