The present-day mass function (PDMF) of field stars in the solar neighborhood is discussed. Major uncertainties in the derivation exist, in partlcular the luminosity-mass relation and the bolometric corrections. Consequently, It is not clear whether the PDMF turns over at very low masses (M < 0.3 Mq), and the slope at the
high-mass end (M > 10 Mq) is more uncertain than usually assumed. The reality of two features in the PDMF (at M = 1.2 Mq and M = 3 Mq respectively) is an open question. Next, the concept of a bimodal IMF is critically examined. Both Gůsten and Mezger's (1983) and Larson's (1986) bimodal models may run into problems. If the effects of high-mass stars prevent low-mass stars from forming, the term "biassed IMF" is a better
description of the situation than "bimodal IMF". The IMF is probably not universal; reported IMF variations in open clusters and globular clusters are unlikely to be spurious. Finally the physics of the IMF is discussed. The. fact that the mass of a star in the making depends on many random-valued (multlplicative) input parameters
suggests a stochastic rather than a deterministic approach for the origin of the IMF.