Moisture balance models for indoor humidity have been developed and used by researchers and practitioners for analysis of humidity levels in existing buildings and for generating realistic interior boundary conditions for building design. These models require as inputs the rates of moisture generation and air exchange, indoor and outdoor temperatures, and outdoor humidity, while handling the effect of moisture storage (moisture buffering) with various levels of complexity. This paper provides a critical review of models in the literature, focusing on the following issues: (i) What are the uncertainties in the various input data required, such as moisture generation rates and ventilation rates? (ii) How accurate are the models for real occupied buildings? (iii) How much is gained by various refinements in the models? (iv) What is the likely effect of common HVAC equipment on indoor humidity?