Abstract Modeling of adsorption processes is vital especially in water treatment processes. To ensure that the right adsorbent is used to remove the target pollutant in water with good efficiency, at the right rate and in the right conditions, mathematical models are employed. Furthermore, these models provide valuable data that are useful in developing an adsorption reactor for large-scale adsorption purposes. Several authors have used these models for providing information about their adsorbents or their adsorption system without any deep understanding of these models. This chapter provides a detailed insight into these mathematical models, their theories and assumptions, and how they are effectively used to provide the needed information that is useful to the scientists and the engineers. This chapter did not consider exactly every mathematical model used for estimating adsorption process. However, it takes into consideration fundamental models and their applications. It is hoped that this chapter provides the scientists and engineers a better understanding of these adsorption models and even those that will be developed in the future.