A review of research which points to the importance of behaviour in energy consumption is presented. The literature on ways of controlling energy consumption by behavioural means is reviewed. Understanding the consumer is highlighted as being important in explaining variation in energy utilization.This thesis investigates the idea that consumption could be reduced through an understanding of people's beliefs. A variety of methodologies was used to this end.(a) People in difficulties with paying their bills, contacted through a radio appeal, were interviewed.(b) Objective measurements of occupant behaviour were obtained which suggested reasons for differences in energy consumption.(c) Using a semi-structured interview and a ranking task a relationship was sought between knowledge of the relative running costs of appliances and energy consumption. Negative relationships were found.(d) Two studies of consumer understanding of Economy 7 electricity bills were undertaken in the public and private sectors. In the former, but not the latter case, a significant relationship was found between the bestunderstanding of Economy 7 and of bills, and lower costs.(e) Semi-structured interviews were used to investigate householder understanding of thermostats in two types of homes: those with gas radiator systems and those with electric underfloor heating.As a result of the studies many suboptimal strategies based on erroneous beliefs came to light. The research reported here has not only enabled practical recommendations to be made for immediate implementation but has also demonstrated the fruitfulness of investigating consumers' understanding of their heating systems as a means of promoting the efficient use of energy.