Motivation is one of the key learner characteristics that determine the rate and success of language learning. It provides the primary impetus to embark upon learning, and later acts as the driving force to sustain the long and often tedious learning process. Due to the complex nature of language itself--it is at the same time a communication code, an integral part of the individual's identity, and the most important channel of social organization--language learning motivation is a multifaceted construct, consisting of a range of different motives associated with certain features of the language, the language learner, and the learning situation. This volume addresses this intriguing complexity by first providing a comprehensive overview of recent developments in the field, and then by offering a selection of data-based studies by prominent motivation researchers. These research papers conceptualize the motivation complex in different yet complementary ways, proposing and empirically validating various constituent attitudes, orientations, and motives.