Vocabulary acquisition has become an extremely important part of second and foreign language acquisition. Nowadays, teachers cannot rely on students acquiring the needed vocabulary just through interaction with the language, and finding authentic ways to engage students actively in the learning process poses one of the greatest challenges in the teaching process. Even though vocabulary acquisition is a learner-centred activity, students enjoy activities and learn vocabulary in collaboration with peers. Since Project-based Learning (PBL) is a method which organizes learning around projects and facilitates learning in context, in collaboration with peers, it can improve language learners' vocabulary learning and acquisition. The current book reviews the key features of PBL and discusses them in the context of vocabulary teaching. It also includes an empirical case study of a PBL project conducted for vocabulary learning of elementary EFL learners in Iran.