This paper provides an integrative summary of a three-year research program investigating various factors pertinent to human operator adaptation in process-control systems. Four longitudinal experiments were conducted with a simplified but representative thermal-hydraulic process simulation. These experiments investigated the impact of four behaviour-shaping constraints that can influence operator adaptation: interface content, interface form, type of training, and pre-existing competencies. The findings obtained from the research program are summarized, and a number of implications for the design and operation of process-control systems are suggested.