Multi-tasking (MT) is prevalent in many work environments. While there are often negative consequences of MT, such as increased error, stress, and turnover, some individuals thrive in MT environments. An assessment tool that predicts performance in different MT environments would be invaluable for personnel selection and assignment. A central purpose of the present research was to investigate variations that exist among MT environments in order to form a better understanding of the demands placed on workers in these different environments. From a review of MT-related literature, and interviews with experts from different Military Occupational Specialties (MOS), we distilled individual differences and environmental variables that affect performance in different MT environments. Based on this research, we created a model of MT environments that varies along three main dimensions: type of MT required (decision-making, information-monitoring, and task-flow management), intensity of MT, and consequences of failure. The model was then used to guide the development of a measurement approach which assesses both MT environments and individuals' ability to perform well in those environments. The purpose, scope, and framework of this comprehensive Multi-Tasking Assessment System are described in the report, as well as a description of additional research necessary for the development of the system.