Sterols: Types, Classification and Structure describes the methodology used to determine sterol content in coral reef food webs, and how sterol data is used in trophic ecology studies. The authors briefly explain the basics of gas chromatography and mass spectrometry as necessary tools to confidently separate, identify, and quantify sterols. Sterols from different sponge families have been described, however, few studies have been conducted involving the sterols of the freshwater sponge compared to those of the marine environment. The number of sterols present varies with the species, and this characteristic make it possible to use this data as a chemosystematic marker. In olive oil, sterols constitute the majority of the unsaponifiable fraction. In recent years, there has been increased interest in the sterols of olive oil due to their health benefits and their importance to virgin olive oil quality. Thus, the authors discuss recent findings concerning the effect of cultivars on the sterolic profile of extra virgin olive oil. The subsequent study aims to contribute to the optimisation and valorisation of virgin olive oil quality in the world olive-producing areas. This work was carried out on the study of virgin olive oil from two new olive varieties obtained through uncontrolled crossings. The sterolic fraction of argan oil is also compared to that of olive oil. The total phytosterol content ranged from 1700.80 mg/kg in chemlali oil to 150.40mg/kg in argan oil. In contrast to chemlali oil in which β-sitosterol is predominant, the major sterols detected in argan oil is schottenol and spinasterol. In closing, the authors examine the analysis of phytosterols, a multistage procedure that includes extraction, isolation/purification as a group of related compounds and a chromatographic technique for separation, identification, and quantification.