T heresa-Marie Rhyne has lately been organizing efforts for a number of researchers to produce lists of top visualization problems, and I am flattered to be included. A recent Visualization Viewpoints column (see the July/August 2004 IEEE CG&A) featured Chris Johnson's excellent list, and now it's my turn. Since the May 1999 VisFiles column 1 already describes my list of the top ten problems that will drive future visualization work, this Visualization Viewpoints column is a look back at the top five problems that drove my own work developing Vis5D, Cave5D, and VisAD (see the "Vis5D, Cave5D, and VisAD" sidebar). Some of these problems are high-minded and some are grubby and gritty. This is the mix of problems that I learned from Verner Suomi, the founder of the Space Science and Engineering Center where I do my visualization work. Suomi was literally the inventor of weather satellites. Among many other technical accomplishments, he held the patent on the spin-scan radiometer, which was the basis for the geostationary satellites that until recently produced the cloud animations we see on TV weather shows. He also lobbied the US congress for the funds to develop these satellites and was heavily involved in building the prototypes. He was a visionary, a politician, and what my father would have called a "dirty-fingered engineer ." I hope these problems reflect this combination of concerns that lead to useful change. I start at number five, and count down to the most important problem.