Legal commentaries are a type of secondary source that provides clarity about the meaning of treaty provisions so they can be appropriately interpreted and applied by practitioners. Since 1870, the International Committee of the Red Cross (ICRC) has produced such commentaries on each successive international humanitarian law (IHL) treaty or update to an existing treaty. Over time, who drafts these commentaries and the methodology behind them has evolved, from early commentaries written by a single jurist who had participated in the drafting of the treaty to multi-authored works based on extensive research and the methodology found in the Vienna Convention on the Law of Treaties. The ICRC Commentaries have always been geared towards those tasked with applying IHL, but this audience has expanded over time, giving them a more global reach, and their reception has evolved accordingly. The most recent iteration of the ICRC Commentaries on the 1949 Geneva Conventions and their 1977 Additional Protocols is currently being produced, with some changes in methodology to guarantee that they remain a practical tool for the interpretation and application of those instruments.