This research is an empirical multiple-case study that is designed to explore adult individual learners’ vocabulary learning processes, and to examine their use of vocabulary learning strategies. It investigates the following key questions: (1) What vocabulary learning strategies do the individual learners usually use to find the meaning of unknown words? (2) What vocabulary learning strategies do the individual learners usually use to consolidate the words? (3) How do the individual learners apply the vocabulary learning strategies for the purposes mentioned above? (4) What are the differences between the learners’ use of vocabulary learning strategies? By using multiple data collection methods – questionnaires, interviews, and think-aloud protocols – I not only investigate what strategies the individual research participants use to study vocabulary, but also look at how they actually employ the strategies while completing a series of vocabulary activities. Finally, I also compare the patterns in the use of strategies between the participants. After the introduction, Chapter Two begins with the clarification of basic terms: “word,” “word knowledge,” and “strategy.” In Chapter Three, studies in the fields of vocabulary learning strategies are reviewed. Chapter Four deals with mental processes involved in vocabulary learning. Chapter Five focuses on the empirical study. I describe briefly the German language course (GER 101) and the language textbook, Vorsprung (2nd edition, 2002), and illustrate in depth the methodology used for data collection and data analysis. The results of the study are presented in Chapter Six. Chapter Seven summarizes the study results, followed by suggestions for foreign vocabulary instruction and for future research. The study illustrates that participants used a variety of vocabulary learning strategies to learn vocabulary. In total, 49 individual vocabulary learning strategies are identified and classified. Further, the differences between the learners are shown to be not only in what strategies they use but also in how they employ them. Finally, the study shows that well-organized and planned learning strategy training should be provided to language learners in order to make sure that they can use the strategies effectively, and that language instructors and the language textbook should play an active role in strategy training.