Commercially available plant-based milks are milk analogues manufactured to mimic the emulsion structural, nutritional, and functional properties of animal milks by combining plant materials extracted from e.g. oat or almond combined with added fats, vitamins and minerals. It is not yet clear how the molecules in plant-based milks interact to form the milk structures or even what the composition of the final products is. The purpose of this review is to bring together evidence relating to the molecular composition of plant-based milks and the structural arrangement of the molecules in the final products. Much of the available work involves chromatographic methods, microscopy, gravimetric, volumetric and elemental analyses methods. Although confocal microscopy with fluorescence labelling has been used to stain for different molecules in milk, there is little information on inter-molecular interactions. There is thus a need for new methods to investigate component interactions to ensure the maintenance of plant milk product quality.