The current study examined teachers' perceptions of online and blended professional development and their implementation of acquired learning in the classroom. Interviews with K-12 teachers from across the United States revealed key themes and implications for professional development practices. Collaboration emerged as a crucial element, with teachers emphasizing the value of working collaboratively, sharing ideas, and engaging in meaningful discussions. This collaborative engagement was seen as essential for enhancing teachers' understanding and knowledge acquisition. Strategic planning and relevance were also highlighted as significant factors in professional development, emphasizing the need to align learning experiences with classroom expectations and practical application. The current study further demonstrated the transformative nature of online and blended professional development, with teachers reporting positive changes in their approaches and planning, resulting in improved teaching effectiveness and enhanced student experiences. These findings contribute to the understanding of effective professional development in online and blended learning contexts, emphasizing the importance of collaboration, strategic planning, and transformative experiences. The current study calls for the development and implementation of professional development programs that prioritize these elements to foster positive changes in teaching practices and improve student outcomes. [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.]