This chapter uses the major contributions of Bob Karplus to develop several important themes that have emerged in the past five decades of curriculum and instruction in science. The chapter begins with a perspective on curriculum development and curriculum developers. A second theme is the importance of identifying major scientific concepts as a foundation for the curriculum. A third theme addresses the importance of incorporating research on learning theory into designs for curriculum and instruction. Finally, there is a theme of curricular reform and the professional development of science teachers.