Catalyzing Change in Middle School Mathematics is part of the Catalyzing Change Series, a collection of three books intended to initiate the critical conversations on policies, practices, and issues that impact mathematics education. In 2018, the first book in the series, Catalyzing Change in High School Mathematics: Initiating Critical Conversations, was published. The work initiated by that book suggested a need to broaden the critical conversations to include early childhood, elementary, and middle school mathematics. For example, the recommendation for a common shared pathway in high school mathematics must take into consideration what must happen in early childhood, elementary, and middle school mathematics for a common shared pathway to become a reality in high school mathematics. Catalyzing Change in Middle School Mathematics: Initiating Critical Conversations recognizes that the needs of young adolescents are different from elementary and high school-age students and that policies, practices, and issues must consider the unique needs of this student group. Students undergo significant developmental changes from elementary school to middle school. These changes contribute to how they see and understand the world as well as how they see and understand their place in the world. Critical conversations that middle school teachers need to initiate should center on the following serious challenges: Broadening the purpose of school mathematics' focus to include the development of positive mathematical identities so that students can make purposeful decisions about their future endeavors; Dismantling structural obstacles that stand in the way of mathematics working for each and every student Implementing equitable instructional practices to cultivate students' positive mathematical identities and strong sense of agency; Organizing middle school mathematics along a common shared pathway grounded in the use of mathematical practices and processes to coherently develop deep mathematical understanding.