Supercritical fluids with both gas- and liquid- like properties have been adopted as an extraction media to isolate many useful substances from various types of complex matrices. Compared to conventional extraction methods, supercritical fluid extraction is preferred because it can be simple, fast, inexpensive, effective and selective. Although the most common supercritical fluid is pure or modified carbon dioxide because of its low critical temperature, inertness, non-toxicity and cheapness, a number of alternative compounds, such as nitrous oxide, ethane and water, possess critical properties that could permit convenient applications in SFE. This review firstly describes the basic science of supercritical fluids including thermodynamic properties and their effects on the choice of supercritical fluids for extraction applications. The advantages of supercritical fluid extraction and its applications in various areas such as environmental remediation, food processing, pharmaceutical and cosmetic products, and many other applications are examined. The current state of development of supercritical fluid extraction systems and equipments are summarised and compared and future direction for research on SFE are discussed.