Changelings are an alien race from the Star Trek universe. They are called Changelings because of their ability to shape-shift. The Changelings were introduced in the Star Trek spin-off Star Trek: Deep Space Nine. Constable Odo, one of the regular characters on that show, is a Changeling.

Their natural state is a liquid protoplasm. The Female Shapeshifter once told Odo that their race once had bodies similar to those of other species, but they had since evolved beyond those physical bodies. Changelings have the ability to meld together (in a process known as "linking") to share information and emotions in a very intimate manner. The Changeling homeworld is covered in a sea of Changelings known as the Great Link.

Changelings can turn themselves into almost anything and can flow through any gap in their liquid state. When they assume a different shape, such as a rock, scanners will show them as a rock. Changelings who have sufficently disciplined their shapeshifting abilities are able to turn themselves into convincing imitations of others. However, if a part of a changeling is separated from the whole, it reverts to the liquid state. In addition, a Changeling must regenerate, returning to its liquid form once every eighteen hours.

The Changelings are native to the Gamma Quadrant. All but one hundred of the Changelings are Founders, the rulers of the Dominion. (Odo is one of The Hundred). They seek power because they were once persecuted by non-shape-shifters, whom they call "Solids." After the discovery of the Bajoran wormhole and the subsequent war between the Dominion and the United Federation of Planets, the covert Federation group Section 31 created a disease that prevented the Changelings from shape-shifting. When the Dominion was defeated, the Changelings were cured.