The rapport building phase of child investigative interviewing is referred to in practice guidelines as an essential. Nevertheless, in contrast with other aspects of the interview it has been subject to little empirical examination. There is a lack of information on the rapport phase's impact on children's communication and whether this changes across a variety of different circumstances. Finally, few researchers have empirically assessed different styles of rapport building. This thesis investigates the communicative influence of the rapport building phase in child investigative interviews. It also examines the effectiveness of a new collaborative play approach to rapport building with respect to its influence on children's communication and the rapport levels between the interviewer and child. The investigation began by interviewing practitioners about their perceptions and experiences of rapport building practice, and their opinions on the use of play during the rapport phase. A grounded theory approach to analysis found that interviewers perceive the rapport phase as a tool for facilitating communication with children during the investigative interview. This is achieved in three main ways: (1) assessing the child during the rapport phase, (2) adjusting interview approach based on the child's presentation during the rapport phase, and (3) producing a psychological outcome in the child that then facilitates communication. The resultant theory and the comments made about play rapport were used in subsequent experimental chapters to design and implement play rapport, and to interpret the empirical findings. The second line of enquiry investigated the communicative impact of a collaborative play approach to rapport building in adult-child interactions. Children across three different age groups (6-7, 8-10 & 12-14 year olds) were more communicative and demonstrated greater rapport with an adult after play rapport than children in a control condition. The findings indicate that a collaborative play format of rapport building is an effective communication facilitator. The third empirical study tested play rapport's efficacy in a mock investigative interview situation. It was compared with the current open style of rapport building used by practitioners in the UK, and a control condition that involved no rapport phase. Older children (8-10 year olds) who experienced play rapport demonstrated information benefits in comparison with children in the control condition. No differences were found between the open style and the control, and the open style and play rapport for information detail or accuracy. Children (5-7 and 8-10 year olds) were however, more resistance to interviewer suggestion after engaging in a play rapport phase in comparison with children who experienced the open style of rapport building. These results indicate the potential of play rapport as a communication facilitator for children in investigative interview settings. The final empirical chapter examined anxiety data taken from the children during the third study. This was to address the hypothesis that improvements in recall as a result of the rapport phase, and in particular play rapport, were due to a reduction in the children's anxiety levels. The data showed no differences across the rapport protocols in terms of anxiety for any of the measures. The information benefits found could therefore not be explained with respect to a reduction in anxiety. Alternative theories were then proposed, and future research outlined that could further investigate the psychological underpinnings of the communicative effects of the rapport phase, and the collaborative play rapport approach. .