The genus Iris is the predominant member of the Iridaceae family in the Northern Hemisphere. There are about 300 species worldwide, occurring in North America, Asia and Europe. At least one species, Iris setosa, is circumpolar, occurring in Sibera and in Canada.

Different Iris species are native to every environment, from woodland to desert to swamp to steppe and tundra.

This genus is often broken up into several genera, such as Juno for the juno irises, but we will treat these as subgeneric groups of the genus Iris. The most common garden iris have been the bearded hybrids, often called Iris x-germanica. Other common types of iris found in gardens are Siberian iris hybrids derived from Iris sibirica, and Japanese iris hybrids derived from Iris ensata. In some areas, hybrids of the several species of Louisiana irises are grown in gardens.

In eastern North America, the crested iris, Iris cristata, grows in woodlands. Two species of iris, I. virginica and I. versicolor, grow in eastern North America in open, wet or boggy areas. I. virginica is found in the southern portion of their range, and I. versicolor is found in the northern part.