  We summarize the collective knowledge of physical and surface properties of
comet nuclei, focusing on those that are obtained from remote observations. We
now have measurements or constraints on effective radius for over 200 comets,
rotation periods for over 60, axial ratios and color indices for over 50,
geometric albedos for over 25, and nucleus phase coefficients for over 20. The
sample has approximately tripled since the publication of Comets II, with IR
surveys using Spitzer and NEOWISE responsible for the bulk of the increase in
effective radii measurements. Advances in coma morphology studies and long-term
studies of a few prominent comets have resulted in meaningful constraints on
rotation period changes in nearly a dozen comets, allowing this to be added to
the range of nucleus properties studied. The first delay-Doppler radar and
visible light polarimetric measurements of comet nuclei have been made since
Comets II and are considered alongside the traditional methods of studying
nuclei remotely. We use the results from recent in situ missions, notably
Rosetta, to put the collective properties obtained by remote observations into
context, emphasizing the insights gained into surface properties and the
prevalence of highly elongated and/or bilobate shapes. We also explore how
nucleus properties evolve, focusing on fragmentation and the likely related
phenomena of outbursts and disintegration. Knowledge of these behaviors has
been shaped in recent years by diverse sources: high resolution images of
nucleus fragmentation and disruption events, the detection of thousands of
small comets near the Sun, regular photometric monitoring of large numbers of
comets throughout the solar system, and detailed imaging of the surfaces of
mission targets. Finally, we explore what advances in the knowledge of the bulk
nucleus properties may be enabled in coming years.
