This thesis reviewed the major aetiological and treatment literature on infant sleep disturbance and concluded that the conceptual and methodological limitations of this literature have prevented progress in understanding the phenomenon. A model integrating the major findings of the literature was developed. The ethics of intervening to modify infant sleep disturbance were explored, in preparation for the experimental section. There were four separate studies. The first evaluated extinction as an intervention for infant sleep disturbance and found it effective in reducing all aspects of infant sleep disturbance. These reductions were still evident at three months and two years follow-up. This study contributes to the literature through its use of a systematic multiple baseline design, its inclusion of reliability assessment and by confining its consideration to the more uniform developmental stage of infancy, rather than including infants and pre-schoolers together. The second study evaluated two administration regimes for trimeprazine, a sedative widely prescribed for sleep disturbed infants in New Zealand. Trimeprazine increased the number of nights the infants slept through, however its effect was highly variable and in most cases not clinically significant. There was no evidence that use of the medication at either dose led to a lasting decrease in sleep disturbance. Study Two had the same strengths as Study One, and also contributes to the literature by its examination of a lower dose rate than any previously published study. Study Three compared extinction alone as a treatment, with extinction plus trimeprazine and extinction plus placebo. It aimed to establish whether the use of trimeprazine would lead to less infant distress, more infant security and less parental anxiety during treatment. There was some evidence that the use of the drug led to less infant distress, but an important finding was that infant security and maternal anxiety improved for all treated groups over time. This finding was important given some of the criticisms made against the use of extinction on ethical grounds. Study Four directly measured a wide range of infant behaviours in a group treated with extinction and two control groups. There was no evidence that extinction had any negative side effects and some evidence in fact, that it had positive side effects. This series of studies answered several important questions, particularly regarding the limitations of drug use and the efficacy and safety of extinction. The combination of these two treatments has provided another treatment alternative, particularly where parents are reluctant to use extinction. Several directions for future research were highlighted. These included not only the continued investigation of treatments for infant sleep disturbance, but also the factors determining whether a sleep disturbed infant presents for treatment and the effect of behavioural interventions on the development of infant sleep per se.