It is generally accepted that interpretation plays a significant role in tourism. It can help to enrich visitors’ experience and their cultural and environmental knowledge so that empathy towards conservation, heritage and culture can develop. However, there is a concern that much of the interpretation practised by the tourism industry is of poor quality. Its significance in ecotourism, cultural tourism, wildlife tourism, heritage and adventure tourism, and the concern about its quality gives rise to the need to examine how effective guides are in its delivery, what makes guides effective or ineffective and what continuing education and training they require for effective interpretive delivery. It is against this background that this study was done in order to investigate the interpretive effectiveness of tour guides in South African national parks. The overall purpose of the study was to design a model for effective interpretation for tour guides operating in South African national parks. To accomplish this, an in-depth literature review was done, followed by an empirical investigation. From the literature, the concept of environmental and cultural interpretation was analysed and the constructs that form the theoretical framework for measuring interpretation identified. A conceptual model was formulated that indicates that the effectiveness of tour guides is related to park policies; knowledge and appropriate application of interpretive delivery techniques; management support, evaluation and tourists’ feedback. A mixed method research design was employed, utilizing both qualitative and quantitative methods. In-depth interviews were conducted with nominated officials in the parks to solicit their views on what they perceive as critical issues in the delivery of effective interpretation. Tour guides were surveyed to determine their perceptions of problems with interpretive delivery techniques and their continuing education and training needs in regard to interpretive delivery techniques. Tourists were surveyed to determine their perceptions about their general satisfaction as attributed to interpretation, and the extent to which tour guides applied the interpretive delivery techniques during interpretation. Purposive sampling and convenience sampling techniques were used in this study. Data analysis on the qualitative interviews was done by summarising the content and categorising the statements made by the officials from certain which conclusions could be drawn. These interviews generated certain constructs and variables which were included in the survey instrument. Critical factors for effective interpretation, according to officials, were identified. These included communication skills, continuing education and training, knowledge of the area and a passion for the task. Quantitative data was analysed by ranking those factors which proved to be most problematic in effective interpretive delivery, the most important of which is addressing tourists by their names, using the five senses to enhance the experience, gaining the attention of the tourists, encouraging participation of tourists and presenting the content in a simple manner. Tour guides generally did not rate delivery techniques as being “serious” problems. It was taken into account that tour guides may be reluctant to state the level of a perceived problem in applying effective delivery techniques and to overcome this limitation, questions relating to the need for training in the same delivery techniques were included in the questionnaire. The results indicated a higher level of the need for training than the level of the perceived problem. Tourists were generally satisfied with the tour guides’ interpretation although only a few were not satisfied with the interpretation of tour guides. However, to ensure sustainability, there is a need for continuing education and training in interpretive delivery techniques and interpretive content for tour guides. This study makes a valuable contribution in regard to tourism, in both the academic and the professional (interpretive guiding) spheres. It provides clear guidelines for national parks to improve the quality of the visitor’s experience and should contribute to the achievement of the goals of sustainability. It provides information that will assist officials in the national parks and those who provide professional development training for guides to better understand guides’ need for further training skills in interpretation in South Africa, an issue which has not been adequately researched in this country. The study produced a model that could enhance interpretive delivery techniques of tour guides in South African national parks.