Objective : Two field studies assessed the effects of critical thinking instruction on training and transfer of a complex decision-making skill. Background : Critical thinking instruction is based on studies of how experienced decision makers approach complex problems. Method : Participants conducted scenario-based exercises in both simplified (Study 1) and high-fidelity (Study 2) training environments. In both studies, half of the participants received instruction in critical thinking. The other half conducted the same exercises but without critical thinking instruction. After the training, test scenarios were administered to both groups. Results : The first study showed that critical thinking instruction enhanced decision outcomes during both training and the test. In the second study, critical thinking instruction benefited both decision outcomes and processes, specifically on the transfer to untrained problems. Conclusion : The results suggest that critical thinking instruction improves decision strategy and enhances understanding of the general principles of the domain. Application : The results of this study warrant the implementation of critical thinking instruction in training programs for professional decision makers that have to operate in complex and highly interactive, dynamic environments.