1. Introduction  
2. The XMM-Newton Bright Serendipitous Survey and the HBSS AGN Sample  
2.1. Absorption Properties  
2.2. Redshift and Luminosity Distribution  
3. Cosmological Properties  
3.1. Evolution  
3.2. X-ray Luminosity Functions of Absorbed and Unabsorbed AGN  
4. The Intrinsic Fraction of Absorbed AGN  
5. The Intrinsic NH Distribution in AGN  
6. Comparison with AGN Unification Models  
7. The X-ray Luminosity Function of Compton Thick AGN  
8. Summary and Conclusions