Moisture sorption isotherms describe the relationship between moisture content and water activity in food. This work presents basic concepts related to the sorption thermodynamics of water, the classification of isotherms, “uses and limitations of the models”, and measurement of sorption isotherms for food materials. The most commonly used models in food are Brunauer-Emmett-Teller and Guggenheim-Anderson-de Boer. The success of the Brunauer-Emmett-Teller model is rather qualitative, considering that almost all cases are linear only in a limited rank of water activity from 0.05 to 0.45, as its main applicability is the estimation of surface areas. And, the use of the Guggenheim-Anderson-de Boer model is generalized by its theoretical bases, mathematical simplicity, and ease to interpret; but it is not frequently used when the water activity greater than 0.93.