Whistleblowing is the act of disclosing information from a public or private organization with the purpose of revealing cases of corruption that are of immediate or potential danger to the public. Blowing the whistle involves personal risk, especially when legal protection is absent, and charges of betrayal, which often come in the form of legal prosecution under treason laws. In this paper we argue that whistleblowing is justified when disclosures are made with the proper intent and fulfill specific communicative constraints in addressing issues of public interest. Three communicative constraints of informativeness, truthfulness, and evidence are discussed in this regard. We develop a ‘harm test’ to assess intent for disclosures, concluding that it is not sufficient for justification.  Along with the proper intent, a successful act of whistleblowing should provide information that serves the public interest. Taking cognizance of the varied conceptions of public interest, we  present an account of public interest that fits the framework of whistleblowing disclosures. In particular, we argue that whistleblowing is justified inter alia when the information it conveys is of a presumptive interest for a public insofar as it reveals an instance of injustice or violation of a civil or political right done against and unbeknown to some members of that polity.