Juniperus virginiana, also known as eastern redcedar, red cedar, Virginian juniper, eastern juniper, red juniper, and other local names, is a species of juniper native to eastern North America from southeastern Canada to the Gulf of Mexico and east of the Great Plains. Farther west it is replaced by the related Juniperus scopulorum (Rocky Mountain juniper) and to the southwest by Juniperus ashei (Ashe juniper). It is not to be confused with Thuja occidentalis (eastern white cedar).

Juniperus virginiana is a dense slow-growing coniferous evergreen tree with a conical or subcylindrical shaped crown that may never become more than a bush on poor soil, but is ordinarily from 5–20 metres (16–66 feet) tall, with a short trunk 30–100 centimetres (12–39 inches) in diameter, rarely to 27 m (89 ft) in height and 170 cm (67 in) in diameter. The oldest tree reported, from West Virginia, was 940 years old. The bark is reddish-brown, fibrous, and peels off in narrow strips. The leaves are of two types; sharp, spreading needle-like juvenile leaves 5–10 millimetres (3⁄16–3⁄8 in) long, and tightly adpressed scale-like adult leaves 2–4 mm (1⁄16–3⁄16 in) long; they are arranged in opposite decussate pairs or occasionally whorls of three. The juvenile leaves are found on young plants up to 3 years old, and as scattered shoots on adult trees, usually in shade. The seed cones are 3–7 mm (1⁄8–1⁄4 in) long, berry-like, dark purple-blue with a white wax cover giving an overall sky-blue color (though the wax often rubs off); they contain one to three (rarely up to four) seeds, and are mature in 6–8 months from pollination. The juniper berry is an important winter food for many birds, which disperse the wingless seeds. The pollen cones are 2–3 mm (1⁄16–1⁄8 in) long and 1.5 mm (1⁄16 in) broad, shedding pollen in late winter or early spring. The trees are usually dioecious, with pollen and seed cones on separate trees, yet some are monoecious.

There are two varieties, which intergrade where they meet:

Eastern red cedar is a pioneer species, meaning that it is one of the first trees to repopulate disturbed sites. It is unusually long lived among pioneer species, with the potential to live over 900 years. It is commonly found in prairies or oak barrens, old pastures, or limestone hills, often along highways and near recent construction sites. It is an alternate host for cedar–apple rust, an economically significant fungal disease of apples, and some management strategies recommend the removal of J. virginiana near apple orchards

Eastern red cedar grows in a wide range of climatic and soil conditions. The tree is extremely tolerant of drought due to its extensive, fibrous root system and reduced leaf area. It can be found from droughty, rocky soils with few nutrients to rich alluvial soils with abundant moisture. However, eastern red cedar is almost never dominant on such rich mesic sites due to intense competition with faster growing, more shade tolerant hardwood trees.

Outside of its native range it is considered an invasive species, and it can be aggressive even within its range. It is fire-intolerant, and was previously controlled by periodic wildfires. Low branches near the ground burn and provide a ladder that allows fire to engulf the whole tree. Grasses recover quickly from low severity fires that are characteristic of prairies that kept the trees at bay. With the urbanization of prairies, the fires have been stopped with roads, plowed fields, and other fire breaks, allowing J. virginiana and other trees to invade. Trees are destructive to grasslands if left unchecked, and are actively being eliminated by cutting and prescribed burning. The trees also burn very readily, and dense populations were blamed for the rapid spread of wildfires in drought stricken Oklahoma and Texas in 2005 and 2006. On the Great Plains, expanding red cedar populations are altering the plains ecosystem: a majority of the region's bird species are not present in areas where the tree's land cover exceeds 10 percent, and most small mammal species are not present where land cover exceeds 30 percent.

Eastern juniper benefits from increased CO₂ levels, unlike the grasses with which it competes. Many grasses are C4 plants that concentrate CO₂ levels in their bundle sheaths to increase the efficiency of RuBisCO, the enzyme responsible for photosynthesis, while junipers are C3 plants that rely on (and may benefit from) the natural CO₂ concentrations of the environment, although they are less efficient at fixing CO₂ in general.

Alterations of prairie ecosystems by J. virginiana include outcompeting forage species in pastureland. The low branches and wide base occupy a significant portion of land area. The thick foliage blocks out most light, so few plants can live under the canopy. The needles that fall raise the pH of the soil, making it alkaline, which holds nutrients such as phosphorus, making it harder for plants to absorb them. However, studies have found that Juniperus virginiana forests that replace grasslands have a statistically insignificant decrease to a significant increase in levels of soil nitrogen. J. virginiana forests have higher overall nitrogen use efficiency (NUE), despite the common grassland species Andropogon gerardi having a far higher NUE during photosynthesis (PNUE). The forests store much greater amounts of carbon in both biomass and soil, with most of the additional carbon stored aboveground. There is no significant difference in soil microbial activity.