This thesis attempted to develop a clearer understanding of the social environment surrounding the athlete and the coach in the team sport context. To that end, achievement goal theory served as the main framework of the social environment's interpretation and was studied in relation to the newly developed coach-athlete relationship conceptualisation. The representative frameworks and conceptualisations introducing these two concepts were discussed in Chapter II, along with a review of the relevant literature in the domain of sport. Specifically, the association between athletes' perceptions of the motivational climate created by the coach and athletes' perceptions of the coach-athleter elationship in terms of Closeness, Commitment, and Complementarity, was examined in Study 1, which comprised Chapter III. Results from canonical correlational analysis showed that athletes' perceptions of a task-involving motivational climate were positively associated with high scores on the Closeness, Commitment, and Complementarity elements. Athletes' perceptions of an ego-involving climate were negatively associated with the Closeness, Commitment, and Complementarity elements. These associations were studied at one point in time, with a cross-sectional design. The second study, which comprised Chapter IV, extended Study 1, in investigating these associations across a nine-month academic period. Results from the Latent Growth modelling analysis showed that specific aspects of the task- and ego-involving climate and specific elements of the coach-athlete relationship changed linearly across time, whereas other remained stable. Moreover, it was shown that athletes' perceptions of the coach-athlete relationship predicted later change in athletes' perception of ego-involving climate, supporting the association between these constructs across time. The consistent association between perceptions of the motivational climate and the coach-athlete relationship provided the basis for examining their effects on potential cognitive, affective and behavioural outcomes through comparative models, in Study 3, which comprised Chapter V. The third study's unique contribution lies in the examination of the mechanisms through which such effects took place. Results from Structural Equation modelling analysis showed that both, perceptions of the motivational climate and the coach-athlete relationship predicted, through the satisfaction of the basic needs, substantial variation in athletes' motivation, role ambiguity, satisfaction, and performance. Collective results of all the studies, limitations, future directions and implications are discussed in Chapter VI. The intention of this thesis has been to extend past work on the study of the athletic social environment. An amalgamation and incorporation of motivational theories and a relationship conceptualisation was assumed to aid in a better and more holistic understanding of the athletes' experience of the social sporting context.