We introduce Lesson Play as an imaginary interaction between teacher and students presented in a form of a dialogue or play. We suggest that lesson plays are a valuable professional development tool in preparing for teaching that can be juxtaposed with, or used as a replacement for, traditional lesson planning. The article begins with an examination of the historical roots of lesson planning and then presents limitations of this traditional mode of preparing a lesson. Then, we present an example of a lesson play and discuss the affordances of this novel structure. We illustrate how a lesson play directs teachers' attentions to potential student difficulties, to concept development and to the language of mathematics.