The thesis is concerned with research in the field of human decision-making, concentrating on techniques of gaming for the pursuit of this research. Following an introduction to the work and a statement of the research programme as it was initially conceived, some current ideas in gaming are investigated. The Superior Commander system of game control is introduced. The content of research games is discussed, and the Organisational Control Game, a board war game designed for research, is described. It is shown that the Organisational Control Game and Superior Commander system successfully meet the requirements for a useful research game and gaming methodology. A detailed literature survey of the psychological secondary task technique for assessing mental processing load is presented. It is noted that the technique might be extended to the study of tasks which have a large problem-solving component. A secondary task experiment on such a task, a chess problem task, is described. It is demonstrated that the secondary task approach can provide techniques for the investigation of complex problem-solving and decision-making tasks. A series of plays of the Organisational Control Game, in which the players had had previous military experience, is described. These games are compared with an earlier series of games, in which the players were students. Certain differences in playing style are identified. The research programme is re-examined, and modifications to it are described. The need for a technique for elucidation and examination of an individual decision-maker's perceptions of his decision-making environment is identified. The technique of cognitive mapping is shown to be suitable for this purpose. A cognitive map analysis of a series of games in which the players were serving army officers is presented.