Modeling the binding of metal ions and actinides to natural particles of various origins remains a challenging task. The use of models to understand the speciation and distribution of metals in the environment is essential for predicting metal bioavailability. In this article, we discuss the primary metal–particle interaction models and their limits, with an emphasis on natural organic matter (NOM). These models have varying levels of complexity, but we discuss only those based on parameters that are independent of environmental conditions. We also discuss the application of such models to field predictions.