We review of the physical processes that are expected to play a role in determining the nature of Brown Dwarfs, in particular, the maximum mass for a Brown Dwarf (set by the Hydrogen-Burning Limit), the minimum mass for a Brown Dwarf (usually regulated by the Opacity Limit), and the multiplicity of Brown Dwarfs. In the remainder of the chapter, we describe a range of mechanisms that have been invoked to explain the formation of Brown Dwarfs and their statistical properties. These include turbulent fragmentation, fragmentation of filaments and discs, dynamical ejection of stellar embryos, and photoerosion. The primary contenders would seem to be turbulent fragmentation and disc fragmentation, and the observations needed to evaluate the relative importance of these mechanisms are starting to emerge.