A major affordance of one-on-one mathematics coaching is its potential to provide individualized, contextualized support for mathematics teachers' learning. Coaches can adjust their work to individual teachers by focusing on instructional improvement goals that take account of teachers' current knowledge, practice, and classroom contexts. It is, however, essential that coaches and teachers work to attain productive instructional improvement goals that are both feasible for teachers to attain and likely to result in immediate improvements in students' learning, if attained. In this article, we describe how coaches can identify productive goals for individual teachers and then, on that basis, negotiate goals successfully with teachers, thereby supporting teachers in seeing productive goals as worthwhile. By describing these two processes, we further clarify the forms of coaching-specific expertise central to effective one-on-one mathematics coaching.