What are factors and how important are they in the development and enhancement of English lexical knowledge of pre-service teachers? With strong English lexical (vocabulary) knowledge, teachers develop their communicative competence which is a sine qua non in the delivery of effective classroom instruction. Communicative competence is what teachers need in order to facilitate learning well. Thus, it is of great importance that teachers should have a strong and working English vocabulary which is developed during their pre-service years. This book reveals the factors that contribute to pre-service teachers' acquisition of English lexical knowledge. It shows the current level of pre-service teachers' vocabulary knowledge across campuses of Isabela State University, a leading institution of higher learning in Northern Luzon, Philippines. Moreover, this book consists of research findings that are helpful in establishing and developing a functional teacher education language program in schools that offer teacher-education courses.