Food scientists aim to control the taste and texture of existing food products and to formulate new structures of high quality using novel combinations of ingredients and processing methods. This text describes the physical chemistry and material science underlying the formulation and behaviour of multi-phase food systems and includes: descriptions of new experimental techniques; food colloids research findings; and overviews of conceptual issues. Essential findings are presented and emphasis is placed on the interfacial and gelation properties of food proteins, and the role of colloidal and biopolymer interactions in determining the properties of emulsions, dispersions, gels and foams. Specific topics include: confocal microscopy; diffusing wave spectroscopy; protein-polysaccharide interactions; biopolymer phase separation; fat crystallization; bubble/droplet coalescence; and bulk and surface rheology.