In this chapter, we present an overview of current knowledge about learners’ use and understanding of connectives. In the first part of the chapter, we will see that connectives are notoriously difficult to master for second language learners, because they require an array of complex competences. Learners must know how to use them appropriately in various genres and registers, have a fine-grained understanding of the meaning differences between connectives used to convey similar coherence relations, and also automatize this knowledge so that it is activated automatically during discourse processing, and not only when they consciously elicit usage rules. In the second part of the chapter, we review the important body of studies that have empirically assessed the causes for learners’ difficulties with connectives, and conclude with some recommendations for teaching. We conclude that research on the second language acquisition of connectives contributes to answering important questions, such as what makes connectives difficult to master, and how they are they used across languages.