Everyone who has taken any biology class knows that DNA is the heritable material. However, very few people know the evidence that led to this conclusion. Science is a discipline based on evidence not acceptance based on faith in a teacher or other authority. This book presents the historical and scientific context to understand how we know DNA is the heritable material. Furthermore, how the structure of DNA reveals its function will be discussed. The famous double helix shape foretold how it would be replicated. Two biochemists conducted the research to confirm that each of the two strands serve as template for new DNA synthesis. Despite its central role in cell function, the order of bases in DNA is not the full story. This book also introduces the topic of epigenetics by presenting the first animal experiments that showed epigenetic changes can lead to a change in phenotype even though the DNA is not mutated.