The polymerization of free nucleotides into new genetic elements by DNA polymerases in the absence of DNA, called ab initio DNA synthesis, is a little known phenomenon. DNA polymerases from prokaryotes can effectively synthesize long stretches of linear double-stranded DNA in the complete absence of added primer and template DNAs. Ab initio DNA synthesis is extremely enhanced if a restriction endonuclease or nicking endonuclease is added to the reaction with DNA polymerase. The synthesized ab initio DNA have various tandem repeats. Sequences similar to those of ab initio DNA products are found in many natural genes. The significance of ab initio DNA synthesis is that genetic information can be created directly by protein. The ab initio DNA synthesis is considered a non-specific synthesis in various DNA amplification techniques. In this review, we present the main studies devoted to this phenomenon and introduce possible mechanisms of this synthesis from our current knowledge.