Organic food products are believed to be healthier, safer and more environment-friendly than their conventional counterparts and are sold at premium prices. Consequently, adulteration of organic plants and fraudulent activities for economic profit are increasing. This has spurred the development of sophisticated analytical procedures for testing authenticity. We review the use of multi-element and stable-isotope analysis based on atomic spectroscopy for discriminating between organic and conventional plants. We conclude that inductively-coupled plasma-mass spectrometry, stable-isotope analysis of bulk plant tissue, and compound-specific isotope analysis based on isotope ratio-mass spectrometry are promising tools for documenting the fertilization history of organic plants. However, these techniques are challenged by the potential diversity of fertilization practices of organic and conventional plant production. We therefore recommend that analytical techniques are combined and coupled with chemometrics to develop statistical models that can classify the agricultural origin of plant products.