1. Introduction
2. The Swift–BAT Sample and Data Analysis
2.1. The Sample
2.2. Extraction of Swift–BAT Spectra
2.3. Extraction of the Soft X-ray Spectra
3. General Properties
3.1. Analysis of the 15-195 keV Continuum
3.2. Luminosity Distribution and Spectral Properties
4. Absorption in the Local Universe
4.1. Observed N$\mathrm{_H}$ Distribution
4.2. The BAT Bias and the Intrinsic N$\mathrm{_H}$ Distribution
5. Anti-correlation of Absorption and Luminosity
6. Luminosity Functions of AGN
7. Discussion
7.1. Compton-thick AGN and the Cosmic X-ray Background
7.2. A Receding Torus or a Clumpy Torus Model?
8. Summary and Conclusion