In the 1950s, a phenomenon known as Â“host controlled/induced variation of bacterial virusesÂ” was reported, in which bacteriophages isolated from one E. coli strain showed a decrease in their ability to reproduce in a different strain, but regained the ability in subsequent infection cycles (1,2). In 1965, Werner ArberÂ’s seminal paper established the theoretical framework of the restriction-modification system, functioning as bacterial defense against invading bacteriophage (3). The first REases discovered recognized specific DNA sequences, but cut at variable distances away from their recognition sequence (Type I) and, thus were of little use in DNA manipulation. Soon after, the discovery and purification of REases that recognized and cut at specific sites (Type II REases) allowed scientists to perform precise manipulations of DNA in vitro, such as the cloning of exogenous genes and creation of efficient cloning vectors. Now, more than 4,000 REases are known, recognizing more than 300 distinct sequences (for a full list, visit REBASEÂ® at rebase.neb.com). With the advent of the Polymerase Chain Reaction (PCR), RT-PCR, and PCR-based mutagenesis methodologies, the traditional cloning workflow transformed biological research in the decades that followed.