Immune system contributes to the pathogenesis of cancer. Immunoediting describes a process in which the immune system can recognize transformed cancer cells and establish an anti-tumor response, potentially leading to the selection of less immunogenic tumor cells. Additionally, inflammation may contribute to cancer progression by activating angiogenesis and oncogenic signaling pathways. In colorectal cancer, dense inflammatory infiltrate in tumor samples is generally associated with improved prognosis but this association is dependent on the type of immune cells and their location. In future, increased knowledge on cancer immunology is expected to benefit the diagnostics, prognostication, follow-up and treatment of cancer.