A study investigated the effectiveness of tandem second language learning using electronic mail (e-mail). Tandem language learning refers to a partnership between two learners, each learning the other's native language. The underlying principles of reciprocity and learner autonomy are explored, use of asynchronous communication between individuals for language learning is discussed, and theory on communicative language learning and the role of writing in language learning is examined, and the study is presented. Subjects were seven dyads of native English- and native Spanish-speaking adults of varied second-language proficiency levels, located in Ireland, Denmark, and Spain. Data were drawn from analysis of e-mail messages and a survey of participants. Analysis focuses on choice of language, type of language used, nature of cultural exchange, style and quality of peer feedback, development of language usage awareness, communication strategies, and students' comments and attitudes. Conclusions and areas for further research are discussed. Contains 53 references. (MSE)