This article reviews current research on the use of Web 2.0 technologies in second language (L2) learning. Its purpose is to investigate the theoretical perspectives framing it, to identify some of the benefits of using Web 2.0 technologies in L2 learning, and to discuss some of the limitations. The review reveals that blogs and wikis have been the most studied Web 2.0 tools, while others, such as social networking applications and virtual worlds, have been less frequently explored. In addition, the most commonly investigated languages have been English, Spanish, German, and French. Considerably less research has been conducted on applying Web 2.0 technologies to less commonly taught languages, such as Arabic, Chinese, or Russian. Additionally, the language learning environments afforded by Web 2.0 technologies have greatly broadened the scope of topics explored in computer-assisted language learning (CALL): from earlier research which tended to concentrate on the traditional four broad language skills, to more recent topics, such as learners' identities, online collaboration, and learning communities. Although very few studies surveyed have actually examined students' progress and learning outcomes associated with these tools, the most frequently reported benefit associated with Web 2.0 technologies is the favorable language learning environments they help to foster. Finally, this review found that much research on Web 2.0 technology and language learning is not clearly grounded in theory, and that a number of studies suffer from a set of common methodological limitations. (Contains 5 notes and 8 tables.)