Adlai E. Stevenson High School (AESHS) is a suburban school in Illinois that has been consistently cited in educational literature as an exemplary professional learning community (DuFour et al. 2004; Richardson 2004; Schmoker 2001). How did this happen, and what has been the impact on the science program as a result of this district’s commitment to professional learning? What distinguishes any school or district as a professional learning community (PLC)? The purpose of this chapter is to examine experiences of the science division of AESHS and the vision of the teachers who are members of this science PLC. Four “how” questions guide the discourse: (1) How do science educators develop and sustain PLCs? (2) How do PLCs promote science learning for our students? (3) How do school and professional environments promote and affect science learning communities? (4) How do we measure the effectiveness of science learning communities?