Naphthenic acids (NAs) are widely present in crude oil and oil sands process-affected water (OSPW). NAs in crude oil lead to corrosion problems, promote emulsion formation, decrease oil quality, and deactivate catalysts, making it critical to isolate NAs. Owing to their toxicity and recalcitrance, the existence of NAs induces serious environmental problems and is the primary target for treating OSPW. The current review provides a summary on the properties and adverse effects of NAs and compares existing techniques to separate NAs from crude oil and OSPW. The mechanisms of these approaches as well as limitations are described. Given the environmental impacts of NAs, new, more effective technologies for extracting and treating these materials must be found.