1. Introduction
2. Optical and Near-Infrared Observations and Data Reduction
2.1. Near-Infrared Observations
2.2. Optical Observations
2.3. Near-Infrared Data Processing
2.4. Constructing the $K_{s}$-band Catalog
2.5. Matching the $R z^{\prime}K_{s}$ Catalogs
3. Multi-Wavelength Data Within the XMDS Field
4. A KX-Selected Quasar Sample
4.1. Separating Quasars from the Stellar Locus
4.2. SED Analysis of Quasar Candidates
4.3. The MIR Color-Color Diagram
4.4. Spectroscopy of Quasar Candidates
4.5. X-Ray Properties of the Quasar Sample
4.6. Photometric Redshift Analysis
5. Conclusions