The preamble to the Biological Weapons Convention (BWC) exerts a significant interpretative influence for the Convention as it takes the role of a “legal corollary” to the Convention, and underscores the BWC’s relationship with the Geneva Protocol of 1925. The chapter highlights how preambles, as identified by the Vienna Convention on the Law of Treaties (VCLT), serve as crucial interpretative tools that provide insights into a treaty’s objective and purpose. The BWC’s preamble bridges historic principles with future-oriented commitments, emphasizing its intent to eradicate biological weapons. Furthermore, the chapter presents the preamble’s crucial references to the Geneva Protocol, underscoring its enduring impact despite the absence of explicit non-use provisions in the BWC. The chapter notes the potential of preambular paragraphs to influence the BWC’s implementation, especially concerning biological and chemical weapons' regulatory synergies. Additionally, it underscores the preamble’s inherent call for international cooperation, the enhancement of mutual confidence, and adherence to the UN Charter’s principles. The preamble signifies the interplay across regimes and reaffirms the interwoven nature of arms control and disarmament laws through the BWC and the Geneva Protocol. Looking at the preamble as a “legal corollary” of the BWC helps in recognizing the historical and legal ties between the Geneva Protocol and the BWC, as well as in situating the BWC within the larger system of international law.