Key words.
1. Introduction
2. The XGPS source sample
3. Cross-correlation of the XGPS/2XMM list with optical/IR catalogues
3.1. Cross-correlation with USNO-B1.0 and 2MASS
3.2. Cross-correlation with Spitzer source lists
4. Optical observations
5. Optical identification of a bright source sub-sample
5.1. Stellar identifications
5.2. Cataclysmic variables
5.3. Candidate High-Mass X-ray Binaries
5.4. Candidate low-mass X-ray binaries
5.5. Notes on other unidentified XGPS sources
6. Properties and characteristics of the XGPS source sample
6.1. Log N - Log S curves
7. Discussion and Conclusions