Working memory, the ability to maintain and manipulate information, is a core cognitive function important for everyday life. The capacity of working-memory differs across individuals, with working-memory capacity a reliable predictor of general fluid intelligence, verbal and mathematical abilities, and classroom achievement. However, research has been inconclusive on whether working-memory is a unitary domain-general construct, or multi-component domain-specific construct. Most theories had until recently thought that working-memory was a fixed ability; however, recent research suggests that working-memory is malleable and can be improved through cognitive training. These training-induced improvements have also been shown on untrained cognitive tasks, such as general fluid intelligence, attention, reading, and math. My research examines the structure of working-memory, validates newly designed web-administered working-memory assessments, and investigates the malleability of domain specific working-memory training.