Cells propagate by making copies of themselves via genome replication. Arguably, replication of DNA is the most fundamental and conserved mechanism of all life forms. Cracking the secret of how this process is achieved with the utmost accuracy is the key to understanding the secret of life. When Watson and Crick first proposed how DNA is replicated based on the structure of the DNA double helix more than a half-century ago, many believed that the structure of the machinery that separates the two strands of DNA for replication would be forthcoming. However, the replication machine turns out to be much more complicated than previously imagined because of its large size, its tripartite nature (it is made up of three engines) and flexibility. Structural information for the DNA replication machinery at atomic resolution by conventional methods was not available until very recently with the advent of the resolution revolution of cryo-EM technology.