Responding to an emerging health threat often requires rapid deployment of behavior change communication. Health communication best practices include developing and testing draft messages and materials to ensure that they resonate with and inspire priority groups to act. However, when faced with an emergency health threat, the timeline for these activities can be compressed from months to weeks. This article discusses the rapid development and implementation of a Zika virus prevention campaign for pregnant women in Puerto Rico. The goal of the campaign was to increase knowledge among and motivate pregnant women, their partners and family members, and the community to follow Zika virus prevention recommendations. The steps in campaign development include environmental scanning, concept development and testing, and message testing to ensure development of campaign materials that resonated with and were well-received by key audience groups. The materials adhere to principles of behavior change communication, and offer our insights for development of future campaigns when under time constraints.