Since its inception in the 1960s, the field of second language acquisition (SLA) has sought to document and explore how children and adults acquire a nonnative language. Researchers have investigated the linguistic, cognitive, social, contextual, psychological, and neurobiological characteristics of second language (L2) learning, processing, and use. Typical research questions include: What are the characteristics of learner interlanguage? How do individual differences, such as working memory capacity, impact the learning of an L2? How does the social context (such as stay-at-home vs. study abroad) influence the fluency, accuracy, and complexity of learner language? How do different types of motivation impact the learning process? How is the L2 processed in the learner’s mind and how is this affected by age of acquisition? To investigate these and many other questions, SLA researchers have at their disposal a large array of research designs. In this chapter, we will discuss various research designs, including quantitative, qualitative, and mixed methods traditions. We will also address current works in progress and examine recent topics of concern related to the conducting of research on L2 learning. Finally, we will conclude with future directions for SLA research.