From a teacher's perspective, teacher learning happens through a complex web of learning experiences. However, research on teacher professional development (PD) typically focuses on the direct influence of single activities or programs. PD researchers less often acknowledge the interactive impacts on teacher learning of the multiple experiences teachers have in different contexts. This dissertation works toward a more thoroughgoing ecological framing of teacher PD by bringing forth three dimensions of teacher learning that are often overlooked: scope, interconnectedness, and temporality. The dissertation centers on the type of design that is widely considered high-quality PD -- namely, experiences that are collaborative and situated in teachers' instructional context -- and considers those experiences from the perspective of these three dimensions. In the first conceptual part of the dissertation, I build on sociocultural, ecological, and complexity theories to frame and operationalize an ecological framework for analysis of teachers' conversations. In the second empirical part of the dissertation, I use data from Project SIGMa (Horn & Garner, 2022). The overall project was a research-practice partnership with a PD organization, where we used video to support secondary mathematics teachers' teams in improving their practice. The analysis investigates the role of teachers' previous professional experiences in their collaborative sensemaking. The analysis focuses on two teacher teams, highlighting moments in which teachers invoke previous experiences and resources from remote settings and provides a proof of concept for their transformative potential. I elaborate on how these resources are used across contexts in conversations (interconnectedness), what they are and where they come from (scope), and when they arise in teachers' sensemaking (temporality). The empirical investigation illustrates the ecological framework and its affordances. The focus on scope allows researchers to name and distinguish contexts that are salient to their different studies. The focus on interconnectedness uncovers the interactive relationship between the immediate and broader PD contexts. Finally, the focus on temporality affords the understanding of different phases in learning and extends linear conceptions of progress. Together, these dimensions portray a rich conceptualization of the ways teachers make sense of PD and incorporate changes into their instruction, providing numerous implications for teacher education. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]