IGOs (intergovernmental organisations) are non-state organisations established through international law by treaty. Prominent examples include the United Nations and the World Health Organization. IGO is also sometimes used more loosely to describe NGOs whose scope is international, also called INGOs (international non-governmental organisations).

Industrial food manufacturing refers to the large-scale production of food products by processing companies using highly mechanised assembly lines and according to pre-defined specifications that guarantee the production of a product with a constant quality. Most of these foods are produced for the retail and consumer market.

Intensification refers to a process by which farming systems (for crops or livestock) are reorganised – often through the application of new technologies, economies of scale, and the use of additional inputs, such as nutrients, chemicals, energy and water – in order to produce more of a desired output (e.g. meat) while using less land, human labour, or capital. The result is that the costs of production for a given amount of food are reduced, thereby increasing profits through larger profits per unit of food, or by expanding total consumption through lower prices, enabling more people to buy more. Often, environmental impacts per unit of product are also reduced, but may be counterbalanced by increases in total production. The impacts of intensification processes on animal welfare, biodiversity, and other issues is also a widely held concern.

Intensive agriculture (IA) is often used synonymously with the terms industrial agriculture and conventional farming. IA is generally used to denote farming systems that use modern technologies and economies of scale to maximise yields relative to land use and production costs (e.g. costs of labour, technology, seeds, fertilisers, and pesticides). IA is associated with high use of chemical fertilisers, agrochemicals, and irrigation. This combination of agricultural technologies became common during the Green Revolution in the mid-20^th century and has long been criticized for its high social and environmental impacts.

Interstitial waters refers to water trapped in sediments or in pores (voids or spaces) in sedimentary rocks – rocks formed by the deposition and cementation of material, as opposed to rocks formed by volcanic processes.

An invasive species is a species that is considered non-native or alien to a given ecosystem and whose introduction has caused, or is likely to cause, significant changes to the ecosystem. Invasive species can be seen as a subgroup of non-native species with characteristics that make them spread easily within their host ecosystem. Their impacts on ecosystems are often perceived as negative and harmful. For example, invasive species are typically described as crowding out populations of native species or harming them in other ways such as through predation. Some conservationists are critical of categorising species as native, non-native and invasive species. They point out that species have always travelled from one ecosystem to the other, in many cases enabled by the travels of humans. Some species that are perceived to be invasive in one area can also be near extinction in places where they are considered to be ‘native’ to.

The Intergovernmental Panel on Climate Change (IPCC) is the international body for assessing the science related to climate change. It is administered by the United Nations with participation and decision making from 195 member states. The assessments that it produces provide the basis for government at all levels to create climate related policies.

The island biodiversity theory is a theory developed by North American conservation biologists in the 1960s that states that the richness of species on a given island is predicted by two factors: a) the size of the island and b) its distance from the mainland. The smaller and further from the mainland an island is, the less biodiverse it will be.

Iso-calorific is a term that means to hold the amount of calories in a diet constant, while changing other variables. It is used in research as a way to make meals with different compositions in terms of foods and nutrients, equivalent and comparable in terms of the energy that they provide.

Isotopic signature refers to the ratio of different isotopes. Isotopes are atoms that have a different number of protons and neutrons. For example, most carbon (C) has 6 protons and 6 neutrons, giving it an atomic weight of 12. This form of carbon is known as carbon-12 (or ¹²C). Another stable form of carbon exists with 6 protons and 7 neutrons, giving it a molecular weight of 13, hence it is known as carbon-13 (or ¹³C). Different sources of methane emissions can be composed of different proportions of ¹²C and ¹³C, with fossil fuel sources often containing relatively more ¹³C than biological sources.