There is an urgent public health need to develop more effective and well tolerated treatments for patients with major depressive disorder (MDD); cognitive training interventions aiming to modify cognitive and affective processing abnormalities underlying MDD represent a promising new strategy. This research project translates a well established cognitive bias in major depressive disorder (MDD), working memory bias, into a novel intervention target. In a double-blind, randomized, controlled study, MDD participants undergo 4 weeks of cognitive training sessions, with two sessions per week.