We propose to make an albedo and radius survey of 100 cometary nuclei using IRS PU and MIPS imaging. We focus on Jupiter family comets (JFCs), which have dynamical and evolutionary connections to other Solar System groups: transneptunian objects (TNOs), Centaurs, Trojan asteroids, and extinct comet candidates. However, among these groups, the nuclei of JFCs remain the _only_ group not yet the subject of a detailed mid-infrared survey. Understanding the evolution of comets since formation is crucial for unlocking their secrets about the thermophysical and compositional environment of the protoplanetary disk. An important way to do this is to study comparisons and contrasts among comets, and between comets and related dynamical groups. To this end, we propose a mid-IR survey of JFCs. Our scientific goals are as follows. 1) Measure the thermal emission from the JFC nuclei to calculate their effective radii. 2) Use complementary ground-based visible-wavelength observations to derive the nuclei's geometric albedos. Note that simultaneity for these observations is not needed. 3) Compare the cometary albedo distribution with those of Centaurs, TNOs, Trojans, and extinct comet candidates to gauge the effects of surface evolution. The glaring albedo difference between TNOs and Centaurs versus other groups needs to be explained. 4) Test for correlations between cometary albedos and other properties of the nuclei, such as composition and dynamical age. 5) Resolve once and for all the long-standing question of just how safe it is to assume an albedo for a cometary nucleus. 6) Use these radii to derive a completely new and independent estimate of the current JFC size distribution that will resolve the ongoing debate between several groups. The number of targets in our sample is driven by the need to test recent indications that the size distribution is truncated at radii smaller than 2 km. In such a case, ours would be the definitive study of the JFC size distribution.