  Low-mass dense cores represent the state of molecular gas associated with the
earliest phases of low-mass star formation. Such cores are called
"protostellar" or "starless," depending on whether they do or do not contain
compact sources of luminosity. In this chapter, the first half of the review of
low-mass dense cores, we describe the numerous inferences made about the nature
of starless cores as a result of recent observations, since these reveal the
initial conditions of star formation. We focus on the identification of
isolated starless cores and their internal physical and chemical properties,
including morphologies, densities, temperatures, kinematics, and molecular
abundances. These objects display a wide range of properties since they are
each at different points on evolutionary paths from ambient molecular cloud
material to cold, contracting, and centrally concentrated configurations with
significant molecular depletions and, in rare cases, enhancements.
