The influence of molecular structure upon liquid crystalline properties has received considerable attention, particularly with regard to the effects upon liquid crystalline transition temperatures of introducing lateral substituents into suitable aromatic molecules. The results from such investigations are reviewed. The effects of changing the terminal substituent in the molecule of a liquid crystalline compound are less clear, and results are presentned which show that the smectie and nematic properties are affected quite differently by the same substituents. The situation with regard to terminal substitents is discussed and illustrated by reference to homologous series of liquid crystalline compounds. It is concluded that no single order of terminal group efficiency can be expected to apply to all systems, as the nature of the molecule into which the terminal substituent is introduced plays an important part in determining the effect of the substituent on the liquid crystalline properties.