This Thesis presents a study of galaxies and quasars from the viewpoint of their
optical, infrared and X-ray properties by combining optical data from Gemini and
WIYN with near to far-IR and optical data from the SWIRE survey and X-ray
data from Chandra. This work represents the largest existing optical spectroscopic
survey in ELAIS-N1 with ∽300 reliable spectroscopic redshifts and the largest Xray
survey, in the same field, which has extended the previous X-ray coverage in
ELAIS-N1 by a factor of 12 and has detected more than 600 X-ray sources. Optical
spectroscopy is used both to calibrate photometric redshift techniques and distinguish
between star forming galaxies and quasars. The merged X-ray, optical and
infrared catalogue is used to determine spectral energy distributions and correctly
identify and characterize AGN, star forming galaxies and the link between black
hole growth and star formation in the host galaxy.