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The spectral energy distributions (SEDs) of low-redshift (z) AGN are now fairly well-observed and understood throughout much of the electromagnetic spectrum. The dispersion around the median SED is large and needs to be addressed by models. Key regions which remain under-studied are the far-IR-submm, the EUV and the gamma-ray. At higher redshift, samples remain small but are growing.

The main conclusions are:

Key open questions in the interpretation of AGN SEDs are:

  1. Are the radio-IR SEDs of CDRLQs and LDRLQs different? This is expected if dust dominates the IR emission in LDRLQs and RQQs while the CDRLQs are non-thermal.

  2. What is the true range of SEDs in the AGN population? The relatively unbiassed, hard-X-ray selected samples facilitated by the X-ray satellites AXAF (NASA) and XMM (ESA), both due for launch in 1999, provide the best opportunity for a relatively unbiassed sample. Radio samples are also relatively unbiassed but are largely confined to the radio-loud 10% of the population, which may introduce its own biasses. These samples would allow us to address the following questions:

    1. How important is dust attenuation to the observational properties of AGN?

    2. How important is orientation to the observed properties of RQQs? This question is probably linked to the last one since the distribution of attenuating material is likely to depend on the source orientation. The question may perhaps be addressed by further studying the NLSy1 objects and the possible role of orientation in explaining their properties.

  3. What is the interplay between thermal and non-thermal emission in the near and far-IR? ISO may begin to address this question by observing the IR SEDs of the brightest sources but we will not be able to observe representative samples until SIRTF begins its operation ~ 2002. IR variability studies also address this question and are becoming more possible as IR array technology advances.
  4. Does the SED evolve? More SEDs for high redshift quasars are needed to address this question.

Acknowledgments. I would like to thank the conference organisers for inviting me to present this review and so forcing me to catch up with at least some of the recent literature. I am very grateful to my colleagues at SAO, in particular Martin Elvis, Paul Green, Eric Hooper, Joasia Kuraskewicz, Smita Mathur, Harvey Tananbaum and Marianne Vestergaard for many fruitful discussions. I acknowledge the financial support of NASA contract NAS8-39073 (AXAF Science Center).

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