1. Introduction

2. Multi wavelength Datasets
2.1. X-ray
2.2. Optical, near infrared and Spitzer photometry

3. Identification of X-ray sources
3.1. Chandra-XMM matches and position

4. The XMM-COSMOS multi wavelength catalog

5. Spectroscopic and photometric redshifts and source breakdown
5.1. Spectroscopic breakdown

6. Number Density Evolution

7. Luminous Obscured AGN
7.1. Selection and sample construction
7.2. Hardness ratio and X-ray obscuration
7.3. IRAC color-color diagrams and color indices

8. Luminosity dependence of the obscured AGN fraction

9. A prototypical Obscured QSO at z=1.59

10. Conclusions