Invited review, to appear in "AGN Physics with the Sloan Digital Sky Survey" (July 2003; Princeton, NJ), eds. G.T. Richards and P.B. Hall.
astro-ph/0310905

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Abstract. Active Galactic Nuclei (AGN) are multiwavelength emitters. To have any hope of understanding them, or even to determine their energy output, we must observe them with many telescopes. I will review what we have learned from broad-band observations of relatively bright, low-redshift AGN over the past ~ 15 years. AGN can be found at all wavelengths but each provides a different view of the intrinsic population, often with little overlap between samples selected in different wavebands. I look forward to the full view of the intrinsic population which we will obtain over the next few years with surveys using today's new, sensitive observatories. These surveys are already finding enough new and different AGN candidates to pose the question "What IS an AGN?".

Table of Contents

INTRODUCTION

THE AGN SPECTRAL ENERGY DISTRIBUTION OBSERVED

General Characteristics

Origin of the various components

HOW WELL DOES THE PICTURE FIT?

The Optical/UV Big Blue Bump

IR continuum

Orientation, obscuration and AGN Class

The Effects of Luminosity

Ingredients which determine the Shape of the SED

OUR EXPANDING VIEW OF AGN

REFERENCES