The first person to realise that bacteria have different shapes was a Dutch microscope builder named Antony van Leeuwenhoek. Since then, science has come a long way, and bacteria are classified mainly by DNA sequencing today, but the shapes still play a large role.

Not only is the shape of a bacterium important to the scientist studying it, the shape is also essential to the bacterium itself. Just like most other characteristics of a living organism, the bacterial shape morphology has an evolutionary history. It contributes to its ability to find and absorb nutrients, its movements and the escape from predators. The bacillus rod shape is now believed to be the ancestral form of bacteria.