Carbon nanotubes (CNTs) have been extensively used to extract pollutants from water and wastewater. These advanced materials exhibit exceptional textural properties, notably their remarkable porosity, high specific surface area, hollow and layered structures, and numerous external and internal adsorption sites. Furthermore, their intrinsic properties can be enhanced through covalent or noncovalent modifications by adding specific functional groups to their surface, thereby improving their selectivity toward particular classes of pollutants. This chapter presents the distinct synthesis routes and modification techniques for CNTs, along with insights into the key characteristics to consider when using them as nanoadsorbents for water and wastewater purification. We also bring several examples of systems where different CNTs structures are employed as adsorbents to remove inorganic and organic contaminants. Finally, we discuss the primary challenges of utilizing CNTs as adsorbents in water and wastewater treatment applications.