X
- X PRIZE Foundation
- Xavier Musketeers (basketball)
- Xavier University
- XCEL ENERGY INC
- Xchanging
- XCOR Aerospace
- Xe Services
- Xerox
- XFinity
- Xilinx, Inc.
- XIX
- XL Group
- XL Recordings
- XL Telecom
- XLO-Machine Tools
- XLO-United Clutch Products
- XM Satellite Radio
- Xo - Tronics
- Xobni
- XOMA Ltd.
- Xpress Motorsports
- Xpro India
- Xstrata
- XTC (musician)
- XTO Energy Inc.
- Xylon Loquitur Distillers and Vintners
- Xyratex Ltd.