**Abstract**

This chapter will highlight the advances made in our understanding of the molecular landscape of colorectal cancer (CRC) via the development of molecular subclassification systems and their potential predictive and prognostic utility. Firstly, the comprehensive integrative analysis of 224 colorectal cancer samples performed by The Cancer Genome Atlas (TCGA) Research Network will be described highlighting the potential therapeutic targets identified. The development of molecular subclassification systems primarily via gene expression profile analysis by independent groups will also be described, and their potential clinical and prognostic associations will also be discussed. The chapter will then go on to describe the four consensus molecular subtypes of colorectal cancer which were proposed by an international consortium who applied unsupervised clustering techniques to the independent classification systems previously described. The clinical and prognostic associations of these four subtypes have been explored, and these findings will be discussed. Finally, the utility of molecular subclassification in colorectal cancer will be briefly explored.

**Keywords:** molecular subclassification, consensus molecular subtypes, gene expression profiles, colorectal cancer
