The aim of microbiology is to identify and characterise micro-organisms.  To do this, it is necessary to isolate them and make them multiply in order to study them.

For this purpose, there are a large number of culture media that differ in composition and consistency. A distinction is first made between non-selective and selective media.  Non-selective culture media will be used for the growth of all micro-organisms, these media can be basic or enriched depending on the micro-organisms that you want to grow. Selective media are media that promote the growth of a particular bacterium by inhibiting the growth of undesirable bacteria and allowing the growth of desirable bacteria. There are also media that are used to transport micro-organisms when they cannot be handled at the collection site. These are called transport media.

All these media can be liquid, semi-solid or solid. This difference in consistency is due to the presence or absence of agar, in adequate proportions.