Instructional coaching is a widely accepted form of job-embedded professional development in schools across the United States. The problem is that many new instructional coaches have limited experience facilitating professional growth or working with adult learners. The purpose of this qualitative case study was to explore the perceptions coaches have about their professional learning and how that learning shapes their knowledge, beliefs, and practices. With this knowledge, district leaders can provide for the professional learning needs of their instructional coaches in a way that positively impacts their practice. The work of instructional coaches was examined through the dual lenses of adult learning theory and informal and incidental learning theory. Instructional coaches are also learners and must engage in their professional learning as well as provide learning experiences for other adult learners. A collective case study approach with purposeful sampling was used to identify six participants from the target population of middle and high school instructional coaches assigned to a single school. Data collection methods included a focus group interview, participant reflective activity journal, and semi-structured follow-up interviews. An inductive data analysis process of coding was used to allow themes to emerge. The results included five sources of learning, which informed the six primary coaching practices and three categories of beliefs about teaching and learning, their coaching role, and relationships. Professional development for instructional coaches needs to ensure that training is specific to coaching needs and context, the goals and expectations are in alignment, and the coaches have a network of support and resources. Future recommendations for study include examining perceptions between district-based and school-based coaches and exploring the sources of learning, including how instructional coaches use resources to inform their knowledge, practices, and beliefs. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]