It is commonly stated, by both whistleblower protection laws and political philosophers, that a breach of state secrecy by disclosing classified documents is justified if it serves the public interest. The problem with this defense of justified whistleblowing, however, is that the operative term – the public interest – is all too often left unclarified. This is problematic, because it leaves potential whistleblowers without sufficient certainty that their disclosures will be covered by the defense, leading many to err on the (...) side of caution and remain silent, depriving the public of much-needed information. Failing an agreed upon definition of the public interest or a process to determine it, judges’ applications of the public interest in whistleblowing cases have been criticized for demonstrating ‘judicial idiosyncrasy’. The present paper, therefore, sets out to provide some clarity concerning the concept of the public interest, and to ascertain the extent to which a public interest defense for whistleblowing is feasible and desirable. (shrink)