In this seminar we will review the emergence of single cell genomics and the development of a number of approaches that allow us to analyse the transcriptome and genome of single cells. We will go through a number of applications of this technology in developing cancer treatments, monitoring treatment and disease progression, identification of possible targets in brain cancer, disease mechanisms in examples such as multiple sclerosis. We will also review technologies to sequence the genomes of single cells and how this can help us to understand cancer heterogeneity and resistance to therapy