It is very hard to support effective teaching without good information about actual teaching practice. The MET project has sought to build and test measures of effective teaching so that school systems can clearly understand and then close the gap between their expectations for effective teaching and the actual teaching occurring in classrooms. But good information is hard to produce. It requires the right measures, the right measurement processes, strong communications, and an awareness of how information can be distorted. When given the right type of attention, measures can help set expectations and align effort. It will require care and attention for teacher evaluation measures to serve both professional development and accountability purposes. To help states and districts navigate the work of implementing feedback and evaluation systems that support teachers, we offer nine guiding principles based on three years' of study, observation, and collaboration with districts. Our prior reports tested, and ultimately supported, the claim that measures of teaching effectiveness could be valid and reliable. These principles, explained on the following pages, fall into three overarching imperatives, as shown in Figure 1: Measure Effective Teaching; Ensure High-Quality Data; and Invest in Improvement. Note the cyclical presentation. Well-designed evaluation systems will continually improve over time.