This ethnographic case study examined the roles of district and school macro-culture and teacher sub-group micro-culture in influencing the nature and extent of teachers' professional collaboration. Informed by the sociocognitive theory that learning is rooted in social relationships and develops through interpersonal discourse and activity, the study focused on educators in a middle and high school in one small, rural district. The 41 educators who participated in the study included three administrators, 24 high school faculty members, and 17 middle school teachers. Data collection methods incorporated a general questionnaire, field notes, observations of meetings and gatherings, and extensive interviews. Most of the 21 educators who were interviewed were members of the four sub-groups chosen for in-depth study: the sixth grade and eighth grade teacher teams in the middle school and the English and science departments in the high school. Analysis looked closely at the consistencies and contrasts in the emerging patterns of professional discourse and activity, particularly seeking understanding of the interwoven factors of decision-making and leadership styles, school context dynamics, communication networks and silos, and teacher feelings of professional home. The findings demonstrated the significance of both the academic climate of the general macro-culture and the particular backgrounds and dynamics of members of grade level and departmental sub-groups in the micro-cultures. Within the macro-culture, the study found that empowering leadership styles, sub-group supportive logistical arrangements, a combination of silo and networking communication patterns, and a strong sense of home in the district and school provided a context encouraging productive collaborative interactions. Examining the ways in which membership in particular sub-groups influenced collaboration, the study found that sequential skill-building academic domains, shared leadership and solidarity within the sub-group, conversational routines focused on instruction, and a strong sense of home within the sub-group contributed to purposeful, instruction-based professional collaboration in the micro-cultures. Both the macro-culture of school and district and the micro-culture of the peer-based faculty sub-group exerted considerable influence on the nature and extent of teachers' professional collaboration. [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.]