A field study investigated the relevancy of certain theories in applied psychology for increasing vehicle safety belt use by children. Five different intervention activities applied either extrinsic rewards, or focused on the development of intrinsic motivation (e.g., personal commitment, awareness, active participation). The subjects were 138 children, aged five to eleven years, who attended five 30-min safety belt intervention activities as part of a summer recreation program conducted at three elementary schools. Safety belt use by children and their parents was directly observed and coded by vehicle license number both before and after the interventions. Coupons for free food at a fast food restaurant were distributed to participants by the school personnel, and safety belt use was observed at the restaurant's drive-thru window to assess generalization. The results revealed that participants from all three reward contingency conditions (i.e., rewards for safety belt use, participation, and noncontingent rewards) significantly increased their frequency of safety belt use from the baseline to intervention phase. The parents, although not direct participants in the program, showed similar increases in safety belt use. The increase in safety belt use also generalized to the fast food restaurant for both children and parents; however this effect was transient. Data collected during a three-week withdrawal period indicated that safety belt use decreased slightly among participants rewarded for belt use during the intervention, whereas safety belt use increased slightly for those who received noncontingent rewards or rewards for participation. This finding is consistent with "minimal justification" and "intrinsic motivation" theories and suggests that long-term maintenance and generalization of changes in safety belt use are inversely related to the degree of external control exerted to motivate safety belt use. From an application perspective, this research developed practical community-based interventions for increasing the use of safety belts among children, and demonstrated that behavior change among children may influence the safety belt use of other members in their family. / Ph. D.