A method of authenticating an article, the method comprising: reading a label associated with the article, the label comprising article fingerprint information; retrieving, in dependence on the article fingerprint information, an article fingerprint, the fingerprint describing the resonance response of the article to an excitation signal; applying an excitation signal to the article; receiving the resonance response of the article to the excitation signal; comparing the resonance response to the fingerprint; and determining in dependence on the comparison whether the article is authentic.