Heterogeneous photocatalysis has emerged as a promising tool for the remediation of various pollutants in effluent, with nanoscale metal oxide materials, such as cupric oxide (CuO), garnering robust attention owing to their distinctive size-dependent physicochemical features, as well as their potential applications. CuO has been extensively examined as a promising material for photocatalytic degradation, owing to its non-toxicity, low price, and powerful absorption of a substantial portion of the solar spectrum. However, the performance of CuO has been primarily hindered by the quick recombination phenomena as well as the slow mobility of photogenerated charge carriers. This chapter aims to comprehensively summarize the preparation strategies utilized in the fabrication, modification, and application of CuO-based photocatalysts in wastewater treatment. It also discusses viable strategies to promote their photocatalytic role, such as the generation of ternary and binary heterojunctions by, e.g., incorporating carbonaceous materials and metal ions as dopants, and the integration of other semiconductor materials. Furthermore, it delves into the mechanistic insights underlying the photogenerated charge separation and migration processes, as well as the identification of the functional reactive radical species involved in this process. Finally, the chapter concludes with remarks on the current state of research and the unresolved challenges related to CuO photocatalytic processes, highlighting the future perspectives and research directions in this field.