How can states help ensure that their systems are providing schools and educators with the essential data for improvement efforts? One powerful strategy is to collaborate with partners using a continuous improvement approach. Six states have been doing just that--working together to investigate and address specific, high-priority, high-impact ways to improve their educator evaluation and professional learning systems. The Collaborative for the Continuous Improvement of Educator Effectiveness Systems (the Collaborative), a partnership of the Center on Great Teachers and Leaders (GTL Center), the West Comprehensive Center, and six states (Delaware, Tennessee, Massachusetts, Colorado, Arizona, and Rhode Island), with support from the Northeast Comprehensive Center, have worked together since 2016 to address state-specific design and implementation challenges. Culminating from the work on each state's individual, context-specific problem of practice, the Collaborative developed a set of guiding principles that the six states consider essential for the continuous improvement of educator effectiveness systems. This brief provides an overview of the six guiding principles and presents short vignettes on each of the six Collaborative states that summarize their problems of practice, highlight their continuous improvement efforts within their existing educator effectiveness system, and draw attention to how the six guiding principles were infused into their work.