Wong v The Commissioner of Police & Anor, (1) the High Court released a party from an implied undertaking not to use documents for a collateral purpose. In this case, the documents in question had been provided by the second respondent (the respondent) to the police in support of its criminal complaint against the applicant. Copies of the documents were passed by the police to the applicant during their investigation. While the implied undertaking generally arises in the context of documents that a party is compelled to disclose to another as a result of discovery in a civil action, it can have a wider application to (for example) documents obtained by a party during a criminal investigation. The applicant wished to use the documents in support of her defence to civil proceedings commenced by the respondent. On an exceptional basis and good cause having been shown, the court allowed the applicant's application to be released from the implied undertaking. The case serves as a useful reminder of some general principles in an area of practice that can cause problems for the unwary.