How did we discover that the Universe is Expanding? What does it mean that it is expanding? This lecture introduces Hubble's Law, the observational evidence that the Universe is systematically expanding. As galaxies get more distant from us, the apparent speed of recession gets larger in proportion. The proportionality is the rate of expansion, called the Hubble Parameter (H0). This leads us to the idea of expanding space, and the Cosmological Redshift, which combined with the Hubble Law allows us a way to estimate very large cosmic distances. We will take up the more thorny issue of the Cosmic Distance Scale in tomorrow's lecture. Recorded 2006 February 23 in 1008 Evans Laboratory on the Columbus campus of The Ohio State University.