Aspects of the substellar mass function

The best method we have at the moment for finding the substellar mass function is the study of young clusters. These have the advantages that 1) the stellar mass function for the same environment is known, 2) the brown dwarfs are all at the same (known) age as are the stars, 3) effects of dynamical evolution are minimized the younger the cluster land the brightness of brown dwarfs is maximized). Rather than concentrate on this method, I consider issues relevant to two other methods that are also being employed to study the substellar mass function: brown dwarfs as companions to stars, and brown dwarfs in the field. I argue that the impression of a brown dwarf "desert" that arose from radial velocity studies of solar-type stars is misleading (although there is a "desert island" associated with this class of object). I also discuss the difficulties in finding a mass function in the field, and the use of lithium and luminosity distributions to help constrain it.