Tumour "budding", which is focused on in this book, is generally defined as an isolated single cancer cell or a cluster composed of a very small number of undifferentiated cancer cells in the stroma of the actively invasive front. The correlation of tumour budding with clinical outcome in colorectal cancer was first reported in the 1980s by Japanese surgeons. Since then, the clinical usefulness of this finding in colorectal cancer has been recognised in many countries. Its usefulness has been clarified not only as a prognostic factor and a potential parameter for a grading system, but also as an indicator for therapeutic decision making. Recently, more objective evaluation of tumour budding has been advocated, and the underlying mechanisms of tumour budding formation have been investigated at the molecular level. In this book, tumour budding in colorectal cancer is discussed from various perspectives. This book provides useful information for all investigators trying to deepen their understanding of colorectal cancer and develop evidence-based therapeutic strategies.