•A comprehensive overview of known adulterations in essential oils.•Analytical methodology for detecting adulterations in essential oils.•Overview on fundamental principles and applications of analytical techniques.•Discussion and comparison of advantages and limitations of analytical techniques. Essential oils are natural materials widely used in many fields all over the world and have become an integral part of everyday life. There is increasing demand for essential oils, which has resulted in cases of adulteration. Authentication is thus a matter of critical importance for both consumers and chemical companies. This comprehensive overview covers known adulterations in essential oils, and some analytical methodologies adopted for their detection. We first list recommended tests, and then we explain and discuss common analytical techniques, such as chiral gas chromatography, isotope-ratio mass spectrometry, and nuclear magnetic resonance spectroscopy. We also present (high-performance) thin-layer chromatography, vibrational spectroscopy, coupled and multidimensional chromatography, high-performance liquid chromatography, and combination with chemometrics-metabolomics. This review provides a critical overview of existing techniques.