Inoculum is a substance or material that is used to intentionally introduce an organism into a living environment, usually with the goal of producing a beneficial outcome. This can include bacteria, viruses, plant tissue, and even biological stimulants to encourage growth. Inoculum is typically used in agricultural, pharmaceutical, and biomedical contexts to initiate or enhance a desired reaction. It is especially useful for introducing new species of organisms or organisms with specific traits in order to improve the growth of a particular crop, species, or group of organisms. The benefits of inoculum are manifold. For instance, agronomists often use inoculants to introduce beneficial bacteria or fungi into the soil in order to improve crop yields, reduce weed populations, or provide protection against plant diseases. Inoculants are also used in the pharmaceutical industry to introduce sought-after molecules in order to produce a desired drug or vaccine. There are even commercially available inoculants designed to provide beneficial bacteria to the human gastrointestinal tract to help facilitate digestion or improve the overall health of the microbiome. Inoculating a population of organisms with a foreign one is not without its risks, however. In certain cases, an inoculum may bring in organisms with the potential to cause long-term harm or destruction. Consequently, it is important to understand the source and content of an inoculum before introducing it into a living environment. This is especially true when working with clinical settings, where fresh cultures of organisms must be prepared with exacting precision. In any case, a well-designed inoculum can be an effective way to bring about desired outcomes, such as improved crop yields, drug production, or microbiome health.