This course offers a gentle introduction to DNA, which is having an enormous and growing impact on many aspects of our daily lives such as medicine, agriculture and forensic science. When she was 10 my daughter joked that DNA is the shop next to C & A. What is it really and how were its structure and roles in heredity identified? How was its code cracked and how is it duplicated and decoded in our body’s cells? What has allowed the cost of reading a single human genome to fall from $100 million to $1,000 in only 20 years? How has DNA transformed forensic science and how could it transform agriculture? I shall argue that understanding DNA has had an enormous impact and has an even greater potential. I shall illustrate how it is revolutionising medicine, particularly in my own field of cancer research.