Surveys of the Cosmic X-ray Background
  We provide a highly concise overview of what X-ray surveys and their
multiwavelength follow-up have revealed about the nature of the cosmic X-ray
background (CXRB) and its constituent sources. We first describe early global
studies of the CXRB, the development of imaging CXRB surveys, and the resolved
CXRB fraction. Second, we detail the sources detected in CXRB surveys
describing their identification, classification, and basic nature. Third, since
active galactic nuclei (AGNs) are the main contributors to the CXRB, we discuss
some key insights about their demographics, physics, and ecology that have come
from CXRB surveys. Finally, we highlight future prospects for the field.
