The wide variety of techniques to detect AGN has resulted in a vast array of objects with an enormous variety of selection effects. At high luminosities, optical and X-ray selection seem equally sensitive. At lower luminosities, beam dilution, absorption, and the possible existence of optically-quiet AGN seem to make X-ray selection more reliable. While it may be premature, it seems as if hard X-ray emission is a fundamental observational property of AGN and that the most unbiased samples of AGN are found in E > 2 keV X-ray surveys. This field is rapidly changing, and I anticipate that we will soon have direct comparisons of very sensitive techniques in the X-ray, optical, radio, and IR bands in exactly the same places in the sky to allow the first full view of the AGN phenomena.
Acknowledgments
I would like to thank my collaborators on the Chandra Large Area Sensitive Survey, Len Cowie, Amy Barger, Aaron Steffen, and Yuxuan Yang for many exciting interactions over the last 3 years.