What is a planet? Is Pluto a planet? This lecture traces the debate on the nature of what it means to be a planet by taking an historical approach, looking at how the question has arisen with the discovery of the asteroids and later Pluto and the Kuiper Belt. Many of the issued raised at the 2006 IAU General Assembly meeting were raised two centuries before after the discovery of Ceres and Pallas. We will end with the new definition of a planet, and why Pluto is better understood as a Dwarf Planet, among the two largest objects of the class of small icy bodies of the outer solar system, than as the smallest of the planets. Recorded 2006 Nov 30 in 100 Stillman Hall on the Columbus campus of The Ohio State University.