The Samsung Galaxy S21 is a series of high-end Android-based smartphones designed, developed, marketed, and manufactured by Samsung Electronics as part of its Galaxy S series. They collectively serve as the successor to the Samsung Galaxy S20 series. The first three smartphones were unveiled at Samsung's Galaxy Unpacked event on 14 January 2021, while the Fan Edition model was unveiled at Samsung's CES on 3 January 2022.

The S21 series consists of the base Galaxy S21 model, the larger Galaxy S21+ model, the high-end Galaxy S21 Ultra model, and the mid-range Galaxy S21 FE model. Key upgrades over the previous models, in addition to improved specifications, a display with a 120 Hz adaptive refresh rate, an improved camera system supporting 8K video recording (7680×4320) for the first three models, and a super-resolution zoom of 30–100x, for the ultra model.

The first three phones were released in the United States and Europe on 29 January 2021, while the Fan Edition was released globally on 7 January 2022. The Galaxy S21 FE, S21, S21+, and S21 Ultra launch prices started at $699.99, $799.99, $999.99, and $1079.99, respectively.

The Galaxy S21 was succeeded by the Galaxy S22, which was announced on 9 February 2022