The global water crisis has led researchers to explore various wastewater treatment methods not only to mitigate environmental pollution and but also to assure the reusability of wastewater for further use. Synthetic polymer-based adsorbents are quite useful for successfully treating wastewater, but their high-cost production and non-biodegradability have restricted their uses. Hence, a main focus has been exclusively given on naturally derived chitosan/alginate-based polyelectrolyte complexes (CS/Alg-based PECs) as adsorbents because of their remarkable features such as nontoxicity, biodegradability, biocompatibility, and ease of modification. In this review article, an attempt has been made to systematically evaluate the most recent developments in CS/Alg-based PECs for the wastewater treatment in terms of their formation, stability, patterns of interaction, limitations, physicochemical properties, and trends in removing heavy metals, dyes, etc.