This thesis examines the sales manager's coaching of employees and its effectiveness in the sales context. While some authors maintain that managers would do well to spend more time coaching their sellers to improve their performance, a review of the literature reveals that coaching is still not well defined and that the positive impact of managerial coaching on employee development and performance has yet to be established. Most authors who have addressed the concept approach it from an individual perspective of leadership or management. Though very interesting, this perspective does not take into account the exchanges between the two parties. For this reason, we recommend a theoretical framework based on an interpersonal perspective in which coaching is considered from the point of view of communication and is conceptualized as a developmental interaction between the manager and the seller.This model is supported by the interactivity principle applied to one-on-one sessions between the manager and the seller. We propose a classification of one-on-one sessions that takes into account the following two aspects: the relationship adopted and the coaching process employed. We consider the effect of coaching through the seller's perception. The results of a survey conducted in Quebec's financial services sector support our model. They reveal that seller performance is influenced both by the coaching method and by the type of relationship developed during the coaching sessions. In other words, adopting a structured method and maintaining a partnership relationship with an employee increases the employee's performance. Therefore, in addition to determining for the first time how sellers perceive the coaching practices implemented by their managers, our research allows us to assess the various elements that play a role in improving seller performance. We suggest a number of managerial implications that are supported by the results of our study. Our conclusions draw attention to the value of the practice for the employee who benefits from it and, by extension, for the manager who applies it.