Early hints on the substellar mass function

The study of substellar objects, which had no solid empirical basis as little as two years ago, has now achieved remarkable progress. Three indisputable brown dwarfs have been discovered, and six Doppler companions to solar-type stars appear very convincingly to be extrasolar planets. A number of other Doppler companions are almost certainly substellar. We begin by defining the classes of substellar objects on a physical basis. Then we discuss the discoveries of the past two years, and the methods which led to success. We make a preliminary estimation of the substellar mass function, based on the Doppler results and the cluster searches. We use these to predict the success rate of various continuing searches. We must emphasize that these predictions are based on very few objects, and are likely to change in the coming years. Nonetheless, the number of substellar objects is already reasonably constrained, and it is unlikely that they are a major constituent of the baryonic dark matter.