Abstract: The contents related to appendix and colorectal tumors in the new 5th edition World Health Organization (WHO) classification of digestive tract tumors in 2019 (hereinafter referred to as "the 5th edition") have considerably changed compared with those in the 4th edition WHO classification in 2010 (hereinafter referred to as "the 4th edition"). In addition, contents related to disease evolution in introduction, serrated lesions, polyps and mucinous tumors, and so on have been newly added. The use of the diagnostic name of sessile serrated polyps or adenomas is no longer recommended in the 5th edition; alternatively, it has been renamed as sessile serrated lesions, and the new term "unclassified serrated adenomas" has been included. The term "mixed adenoneuroendocrine carcinoma" has been replaced with "mixed neuroendocrine-non-neuroendocrine tumors, " and the clonal correlation between the two terms has been emphasized. The goblet cell carcinoid is no longer considered a subtype of neuroendocrine neoplasms; hence, it is renamed goblet cell adenocarcinoma. The 5th edition has further improved content on colorectal adenocarcinoma and categorizes vascular infiltration into intramural and extramural (beyond the mucosal muscles) vascular infiltration. Extramural vascular infiltration, whose prognosis is worse, occurs more frequently than intramural vascular infiltration. Tumor budding or the presence of poorly differentiated clusters is considered as an omen of epithelial-mesenchymal transition. Four main consensus molecular subtype groups have been proposed based on RNA sequencing or gene chip technology and the data from the Cancer Genome Atlas and transcriptome profiling. The TNM staging for appendix and colorectal tumors has also been updated in the 5th edition. The changes in the contents of the 5th edition have been summarized to help medical staff become familiar with them as soon as possible.