Proteins and polysaccharides are the two kinds of biopolymers used by food technologists to control structure, texture and stability. In any particular situation, the constituent protein molecules may be attracted towards the polysaccharide molecules (complexation) or repelled apart (segregation). The polyelectrolyte character of milk proteins and hydrocolloid stabilizers like carrageenan and pectin means that electrostatic interactions play an important role in determining mixed biopolymer behaviour. In order to be able to predict how solution conditions such as pH and ionic strength influence food macromolecular functional properties, we need to understand the factors affecting the nature and strength of electrostatic protein–polysaccharide interactions.