Campanula rotundifolia, the harebell or common harebell, Scottish bluebell, or bluebell in Scotland, is a species of flowering plant in the bellflower family Campanulaceae. This herbaceous perennial is found throughout the north temperate regions of the Old World according to the Plants of the World Online database, or throughout the northern hemisphere in other interpretations (see Taxonomy, below). In Scotland, it is often known simply as bluebell. It is the floral emblem of Sweden where it is known as small bluebell. It produces its violet-blue, bell-shaped flowers in late summer and autumn.

The Latin specific epithet rotundifolia means "round leaved". This refers to the basal leaves; not all leaves are round in shape, with middle and upper stem leaves being linear.

Campanula rotundifolia is a slender, prostrate to erect herbaceous perennial, spreading by seed and rhizomes. The basal leaves are long-stalked, rounded to heart-shaped, usually slightly toothed, with prominent hydathodes, and often wither early. Leaves on the flowering stems are long and narrow and the upper ones are unstemmed. The inflorescence is a panicle or raceme, with one to many flowers borne on very slender pedicels. The flowers usually have five (occasionally 4, 6 or 7) pale to mid violet-blue petals fused together into a bell shape, about 12–30 mm (15⁄32–1+3⁄16 in) long and five long, pointed green sepals behind them. Plants with pale pink or white flowers may also occur. The petal lobes are triangular and curve outwards. The seeds are produced in a capsule about 3–4 mm (1⁄8–5⁄32 in) diameter and are released by pores at the base of the capsule. Seedlings are minute, but established plants can compete with tall grass. As with many other Campanula species, all parts of the plant exude white latex when injured or broken.

The flowering period is long and varies by location. In the British Isles, harebell flowers from July to November. The flowers are pollinated by bees, but can self-pollinate.

Campanula rotundifolia was first formally described in 1753 by Carl Linnaeus. As of 2023^[update], no varieties or subspecies of Campanula rotundifolia are accepted in Plants of the World Online (POWO). Several species have been previously described as varieties or subspecies of C. rotundifolia:

Although POWO and World Flora Online (WFO) accept these as separate species, many other sources do not. For example both the Database of Vascular Plants of Canada (VASCAN) and the USDA Natural Resources Conservation Service PLANTS database (PLANTS) do not accept any of these species as valid or even regard them as valid subspecies. This is also the case with authoritative floras such as Flora of Colorado.

While it is now commonly known as harebell or bluebell, it was historically known by several other names including blawort, hair-bell, lady's thimble, witch's bells, and witch's thimbles.

Elsewhere in Britain, "bluebell" refers to Hyacinthoides non-scripta, and in North America, "bluebell" typically refers to species in the genus Mertensia, such as Mertensia virginica (Virginia bluebells).