Colorectal carcinogenesis is a multi-step process during which genetic and epigenetic events determine the transition from a normal cell to a malignant cell. In the past decade, intensive research led to the identification of two types of colorectal cancers that are distinct by their carcinogenesis process. The first group, named LOH (Loss of Heterozygosity) type, is characterized by allelic losses of tumor suppressor genes. The second group, called MSI (Microsatellite Instability) type, is characterized by genetic instability at microsatellite loci. In addition, recent studies suggest the four different signaling pathways, Wnt/Wingless pathway, K-ras pathway, TGF-beta pathway and p53 pathway, could be implicated in tumor progression. In this review we discuss the development of colorectal cancer on the basis of molecular biology and recent advances in research of the colorectal cancer.