Tumour formation in the intestinal epithelium is strongly related to aberrant activity of the Wnt and Notch intracellular signalling pathways. It has been suggested that increased activity of these pathways leads to an expansion of the stem cell (SC)/progenitor cell compartment and reduced differentiation, which ultimately results in hyperplastic growth. The Myb transcription factor, which is frequently overexpressed in colorectal cancer, is involved in homeostasis of the intestinal epithelium, especially in self-renewal and proliferation of the SC/progenitor cell compartment, and interacts with the Wnt-pathway to mediate the expression of genes involved in intestinal stem cell biology. Notch has also been demonstrated to functionally interact with Wnt signalling in intestinal tumour formation and there is an indication that it may similarly interact with Myb. We postulate that the interaction of these three pathways represents a core force to regulate SCs and drive tumour formation in the intestine. By manipulating activity of the pathways in different combinations using compound crosses of transgenic mice, we demonstrate that Wnt, Notch and Myb are equally essential for, and interact in, controlling ISC self-renewal, proliferation and gene expression. By contrast, aberrant activity of Wnt alone is sufficient to drive neoplastic self-renewal and growth, while Notch and Myb remain important for its initiation both in vivo and in vitro. Notch and Myb further interact to regulate differentiation and stem cell gene expression. Thus, this study suggests a shift in the functional hierarchy between Wnt, Notch and Myb during intestinal tumour initiation and progression, which ultimately may influence how novel therapeutic strategies for colorectal patients will have to be orchestrated.