In an uncertain and complex educational environment, teacher leaders play an increasingly important role and are essential to the advancement and success of educational reform and improvement efforts. In this chapter, we examine the concept of teacher leadership and the professional development of teacher leaders within Singapore’s education system. The Teacher Leaders Programme (TLP) was conceptualised and implemented to support the professional growth of appointed Teacher Leaders, as well as to equip them with the knowledge and skills needed to excel in their specific roles. To galvanise the nexus between theory and practice, the Teacher Leader Knowledge Base (TLKB) Matrix and the 5C principles were developed and used to guide the design of the TLP learning experience. Assessment modes focusing on building strong theory–practice links are discussed.