The few examples cited in this section give an indication of the power of coordinated multiwavelength observations for understanding the physical mechanisms at work in AGNs on angular scales far too small to be resolvable with any current or near-term technology. These are difficult programs to implement, but the scientific return on them is potential very large, especially as we can build on the significant progress that has already been made.
I am grateful for support of AGN variability studies at The Ohio State University by the US National Science Foundation through grant NSF-9420080 and by NASA through LTSA grant NAG5-8397. I would like to thank the other lecturers, especially S. Collin and H. Netzer, and my colleagues S.J. Collier, S. Mathur, R.W. Pogge, J.C. Shields, and M. Vestergaard for suggestions on the lectures and the manuscript. I am very grateful for the hospitality extended to me at INAOE, particularly by I. Aretxaga, J. Franco, D. Kunth, and R. Mújica.