Industrial, agricultural, and anthropogenic activities can generally lead to the contamination of waters and wastewaters with various contaminants, including metals, dyes, pesticides, and pharmaceuticals, among others. As water is a key resource for human life, it is fundamental to find alternatives for recycling and reuse. Similarly, wastewaters must be discharged in accordance with established standards to prevent environmental contamination. In this sense, adsorption is an efficient and cost-effective unit operation that can be implemented to remove contaminants from water and wastewater. In this operation, the most important aspect is the adsorbent, as it accounts for approximately 70% of the total cost. In industry, the most common adsorbent is activated carbon. In terms of research, a series of adsorbents are being studied in the literature. Equally, modifications to the adsorbent's characteristics are studied as an important point for improving its potential. Based on our studies on adsorption since 2009, we can conclude that the adsorbent's features can be improved in several ways but mainly by changing the textural characteristics, surface chemistry, and shape; the targets are to increase the adsorption rate and capacity; simplify the phase separation; and allow for a wide range of applications for the adsorbent and decrease its cost. We need to search for fast, simple, and low-cost procedures that cause highly significant improvements.