  The discovery of large numbers of young low-mass stars and brown dwarfs over
the last decade has made it possible to investigate star formation and early
evolution in a previously unexplored mass regime. In this review, we begin by
describing surveys for low-mass members of nearby associations, open clusters,
star-forming regions and the methods used to characterize their stellar
properties. We then use observations of these populations to test theories of
star formation and evolution at low masses. For comparison to the formation
models, we consider the initial mass function, stellar multiplicity,
circumstellar disks, protostellar characteristics, and kinematic and spatial
distributions at birth for low-mass stars and brown dwarfs. To test the
evolutionary models, we focus on measurements of dynamical masses and empirical
Hertzsprung-Russell diagrams for young brown dwarfs and planetary companions.
