<p>Coagulation followed by flocculation is one of the most widely adopted techniques for water and wastewater treatment due to its operational simplicity and high removal efficiency. The process primarily destabilizes colloidal and suspended impurities by charge neutralization and aggregation, forming dense flocs that settle rapidly. Traditionally, aluminum- and iron-based salts such as aluminum chloride, ferric chloride, and polyaluminum chloride are used as coagulants. However, their limited polymeric species and residual metal release restrict treatment efficiency and raise environmental and health concerns. In recent years, significant attention has shifted toward the development of composite or hybrid coagulants that integrate the benefits of both inorganic and organic components. These include inorganic–inorganic (e.g., polyaluminum ferric chloride, PAFC) and inorganic–organic systems (e.g., PAC–polyamine, PFS–PDADMAC, HAPAM), which exhibit superior charge neutralization, floc formation, and sludge reduction characteristics. This review critically compares conventional and hybrid coagulants, emphasizing their synthesis strategies, speciation behavior, and coagulation–flocculation mechanisms. Furthermore, the paper highlights performance evaluation methods and emerging research directions aimed at designing high-efficiency, environmentally benign coagulants for sustainable water treatment applications.</p>