This chapter begins with a look at mental models, theories of practice, and a conceptual model for understanding organizational leadership. Leadership is a purposeful process based in relationships that uses influence to accomplish goals that both the employees and the organization share. Despite competing viewpoints on leaders and leadership processes, all share these core elements. As organizations, schools need robust and effective leaders—not only in the superintendents' or principals' office but also at every grade level, in every department, and in every classroom—if students are to learn what they need for civic responsibility, meaningful, well-compensated employment, and life-long education. An educational leadership theory of practice includes the cognitive structures, processes, and behaviors that make up effective instructional leadership in schools. The chapter concludes with a look at the changing principalship, the 2015 Professional Standards for Educational Leaders (PSEL), and the implications for education leaders.