As a subset of the Phylum Gymnosperm, the division of Pinophyta, and in the Class Pinosida, there are four extant (living) Orders: Araucariales, Cupressales, Pinales and Gnetales, and at least three extinct orders: Cordaitales, Palissyales, and Voltziales.

Contained in these four extant orders, there are ten families, about 60-65 genera and some 650 extant species.

All of these six hundred plus species have the characteristics of being: perennial woody plants, most are trees with a few being shrubs, vascular (having a system of channels for carrying fluids, such as sap), cone bearing seed producing and non-flowering

Although the total number of species is relatively small, the class of Pinopsida, commonly called conifers are ecologically important. This is because they are the dominant plants over large areas of land, most notably the taiga (commonly called the boreal and/or snow forest) of the Northern Hemisphere, but also in similar cool climates in mountains further south.

Boreal conifers have many wintertime survival adaptations. The primary adaptations of these northern conifers is there form, which is a narrow inverted conical shape, together with their downward-drooping limbs, all helps them shed snow. Many of them seasonally alter their biochemistry to make them more resistant to freezing.

While tropical rainforests have more biodiversity and turnover, the immense conifer forests of the world represent the largest terrestrial carbon sink. Conifers are of great economic value for softwood lumber and paper production.