A study of theoretical aspects of tablet lubrication has been carried out in an attempt to elucidate the mechanism of lubricant action and the relationships that exist between chemical structure and lubricating properties. The results of this study indicate that the mechanism of lubricant action, as described for other systems, may be applicable to tablet lubrication. Thus, lubricants may generally be divided into two groups; the first known as fluid- (or hydrodynamic) type which is exemplified by hydrocarbons and the second, termed boundary-type lubricants such as the metallic stearate salts. There appears to be correlation between chemical structure and lubricant efficiency in the tablet-die wall system. The effectiveness of fluid-type lubricants appears to be related to the viscosity of the material used. In this system paraffin was more effective than liquid mineral oil. The evaluation of other classes of compounds revealed that metallic salts of fatty acids were generally the best lubricants while fatty acids, fatty alcohols, alkyl sulfonates, fatty amides, and certain poly vinyl and polyethylene glycol derivatives exhibited good lubricating properties. However, silicone resins, inorganic salts, proteins, carbohydrates, and many metal oxides displayed no lubricating properties. Included in the paper are the results of a survey in which 70 materials were evaluated as tablet lubricants.