Gynoecium (from Ancient Greek γυνή, gyne, meaning woman, and οἶκος, oikos, meaning house) is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules. They did this by folding and fusing at their edges to form a chamber in which the ovules develop. In many flowers, several to many carpels are fused into a structure that resembles a single carpel. The term gynoecium is useful because it refers to the ovule producing structure in a flower, whether it is a single carpel, multiple unfused carpels or multiple fused carpels. In a typical flower, the gynoecium is the innermost whorl of structures and is surrounded by the androecium (stamens) and then by the perianth (all the petals and sepals). In imperfect or incomplete flowers the androecium and perianth, respectively, may be absent. The gynoecium is often referred to as female because it gives rise to female (egg-producing) gametophytes, however, strictly speaking sporophytes do not have sex, only gametophytes do. Flowers that bear a gynoecium but no androecium are called carpellate. Flowers lacking a gynoecium are called staminate.

A gynoecium may consist of a single carpel, multiple distinct (unfused) carpels or multiple connate (fused) carpels. Each carpel typically contains one or more ovules. During pollination, pollen is deposited on the gynoecium (typically on a stigma). Successful germination of pollen and growth of pollen tubes results in fertilization of ova. There is typically one ovum in each ovule. After fertilization, ovules develop into seeds, and the gynoecium forms the pericarp of the associated fruit. Gynoecium development and arrangement is important in systematic research and identification of angiosperms, but can be the most challenging of the floral parts to interpret.