Authentic Lavandula angustifolia (lavender) essential oil samples (n = 41) were procured from six producing countries. Essential oils were analyzed to determine physical properties and to determine profiles and related data by GC/MS, GC/FID, enantioselective GC, and GC/IRMS. The current study identified 43 volatile compounds that were detected in all authentic lavender samples (n = 41), and which can be considered authentic markers. Enantiomeric ranges for 15 volatile compounds and stable isotope ranges for four prominent compounds were determined in authentic lavender. Authentic samples and associated data were used to assess the quality of commercially available lavender essential oil samples (n = 12). 75% of the commercial samples studied were adulterated,and 17 volatile compounds were detected in these samples which can be considered markers for adulteration. This study establishes the utility and importance of using a multifaceted analytical approach to differentiate quality and determine authenticity of lavender essential oil.