This issue hones in on professional development in four key sectors affecting children, youth, and families--K-12 education, early childhood education, child welfare, and youth development. Though these sectors face many of the same professional development challenges, each has its own unique issues, strengths, and goals. The staffing shortage in the child welfare sector, for instance, has spurred public agency-university partnerships to educate workers and increase work force retention. This issue offers new and innovative approaches to professional development--including coaching, a cascade model, online professional development, and the case method--and describes how these efforts are being evaluated. Articles in this issue include: (1) From the Director's Desk; (2) Workforce Development; (3) Evaluating Impact; (4) School-Level Practices; (5) Classroom Assessment Tool; (6) Measuring Online Learning; (7) Child Welfare Partnerships; (8) Site-Based Coaching; (9) Engaging Stakeholders; (10) A Conversation with Thomas Guskey; (11) The After School Workforce; (12) Thinking Like an Educator; (13) Best Practices in After School; (14) Early Literacy; (15) Theory of Action; (16) Building a Tool Kit; (17) Cascade Model; and (18) New and Noteworthy (an annotated list of papers, organizations, initiatives, and other resources related to this issue's theme). [This issue was also funded in part by the Marguerite Casey Foundation and the W.K. Kellogg Foundation.]