Bacteriophages are the most widespread entities on earth, which are able to invade prokaryotes. Bacteriophages play roles in dynamics of bacterial population, pathogenicity, epidemics and evolution. Bacteriophages are taxonomically categorized into two major orders of Caudovirales and Ligamenvirales, five families, nine subfamilies, 145 genera and 684 species; from which, family members of Siphoviridae, Myoviridae, Podoviridae and Inoviridae are the most widespread bacteriophages in nature. Bacteriophages are morphologically categorized into two main categories of tailed and polyhedral, filamentous or pleomorphic bacteriophages. They can have either a single or double stranded DNA or RNA genome. The current review generally introduces bacteriophages using illustrations.