The interaction of biopolymers is of direct importance for the macroscopic properties of food products such as: flow, stability, texture and mouth feel. Here we consider two categories of biopolymers, i.e. proteins and polysaccharides. We will not discuss nucleic acids or synthetic polymers, made by polymerizing simple molecules. However, what is said about proteins and polysaccharides will hold mutatis mutandis for other polymers as well.