Educating students to relate harmoniously with people from different backgrounds has become an important agenda for student affairs professional because of the increasingly diverse nature of the American society. The purpose of this study was to assess how American and international college students develop mature interpersonal relationship skills. All the participants were from a mid-sized comprehensive institution in the Southern United States. The two main constructs measured were tolerance and quality of relationships. Attempts were also made to identify other predictors that may influence mature interpersonal relationships: gender, age, educational level, and academic achievement as measured by GPA. Both quantitative and qualitative data were collected. A sample of 93 international and 93 American students completed the Mines-Jensen Interpersonal Relationships Inventory to collect quantitative data. Using MANOVA for statistical analysis, this study revealed statistically significant differences between American and international students' self-reported levels of tolerance and quality of relationships. Also, there were no statistically significant differences in the self-reported levels of tolerance and quality of relationships between male and female students. Multiple regression analysis was also conducted to determine whether the independent variables (GPA, educational level, and age) predict students' self-reported levels on tolerance and quality of relationships. There were no statistically significant relationships between all the independent variables and students' self-reported levels of tolerance. Statistically significant relationships were identified by senior status and GPA less than 2.0. Senior status positively predicted student's self-reported levels of quality of relationships whereas GPA less than 2.0 was negatively related to quality of relationships. Qualitative data were collected using interviews in order to gain broader perspectives about the development of mature interpersonal relationships. Five international students and five American students were recruited to participate in the study. Responses on how international and American students develop mature interpersonal relationships were quite similar. Also, international and American students noted that the college environment expanded their views about diversity, through meeting of diverse spectrum of students with varied ideas or beliefs. However, international and American students noted different views about how student affairs professionals could enhance tolerance among students from different backgrounds. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]