With uses in fields such as medicine, agriculture, and biotechnology, halogenases are useful enzymes in nature which add or substitute halogens onto other molecules. By doing so, they become necessary for biosynthesis and cross-coupling reactions. Halogenases can be classified by three main types of mechanisms: nucleophilic, radical, and electrophilic. From there, they can be further broken down by the halogen involved, the substrate needed, other proteins used, or molecules generated. A notable example is PrnA which is a tryptophan-7 halogenase that falls under the flavin-dependent definition with an electrophilic mechanism. Historically, research on these enzymes was slow until the use of bioinformatics rapidly accelerated discoveries to the point where halogenases like VirX1 can be identified from viruses. By reviewing the literature available on halogenase since their first analysis, a better understanding of their functions can be obtained. Also, with the application of bioinformatics, a phylogenetic analysis on the halogenases present in cyanobacteria can be conducted and compared.