The study aims to identify single or composite predictors of treatment outcome in patients referred to the Danish treatment packages for first-episode unipolar depression. To do so, we will collect a wide range of demographic, psychometric, clinical, cognitive, biological, and neuroimaging data from a large cohort (1200) of patients when they are first diagnosed with MDD. As an essential part of this study, we will combine collected data with information from various health and social registers, allowing us to follow and characterize the patients before, during, and after treatment. Together, this will enable us to identify clinically relevant treatment response predictors, which will aid treatment choices and ultimately improve patient care.