Zachary Mainen is a neuroscientist whose research focuses on the brain mechanisms of decision-making. He studied psychology and philosophy at Yale University, received his doctorate in Neuroscience from the University of California, San Diego, and held a faculty position at Cold Spring Harbor Laboratory, New York, before moving to Lisbon, Portugal in 2007 to found the Champalimaud Neuroscience Programme and Champalimaud Research, where he held the position of Director and Co-Director until 2019. His work has been recognized by two Advanced Investigator Grants of the European Research Council and the election to the European Molecular Biology Organization. Mainen’s research explores brain function, especially decision-making, using theory-driven experimental approaches. His laboratory helped to pioneer the use of quantitative behavioural paradigms in rodents and combines those approaches with electrophysiological, optical and genetic techniques to study neural representation and computation. A major focus of this work has been toward understanding the function of the serotonin system in the brain and its role in behavior.