The theoretical models for the application of low-field nuclear magnetic resonance (LF NMR) to the cementitious materials are reviewed, in response to the three common questions, namely the data reliability, result stability and model validity problems. The major applications, including the characterization of pores, the quantification of hydration products and the diffusion dynamics, are linked to four theoretical models, namely the two-fraction fast-exchange model, the Korb model, the amplitude model and the cryoporometry related Gibbs-Thomson model. In addition, the limitations in models as well as in instruments are pointed out. In particular, for the mentioned applications, most commonly used pulse sequences together with recommended parameters are provided. Based on the latest progress in the field, challenges and outlooks are discussed.