X series or xSeries or Series-X or variation, may refer to:
- BMW X-series vehicles, see List of BMW vehicles
- Fujifilm X series, a series of digital cameras
- IBM/Lenovo X series
- IBM System x, previously eServer xSeries
- ThinkPad X series, a series of laptops
- Intel Core X-Series, a series of computer CPUs, under the Core brand from Intel
- Nokia Xseries, a family of mobile phones.
- Northgate SeriesX, a line of computers from Northgate Information Solutions
- Sony X series
- Sony Ericsson X series, a series of cell phones
- Sony Vaio X series, a series of laptops
- X (video game series), a space combat and trading game series
- X the album, a series of Christian rock compilation albums
- X-Men (film series) (2000-2020, FOX), frequently called the "X" films, both X2 and X3 being so named
- X-planes, a series of US experimental aircraft
- Xbox Series X, 9th generation videogame console from Microsoft
- Yamaha's X-series motorcycles