In an attempt to explore an environment for language learning that tandem learning via real-time chat affords to foreign language learners and how language learners respond to those affordances, this study examined learner interaction in online Korean-English Tandem Learning with focus on how tandem learners engaged in peer assistance and how they achieved intersubjectivity in the process of their collaborative language learning dialogue. Twelve Korean-American dyads (Korean learners of English and American learners of Korean) carried out 10 rounds of Chat via Moodle@ TC. Chat transcripts produced over the period of 10 weeks were examined with focus on collaborative language learning dialogue, and further analyzed into the categories of peer assistance, intersubjective moves, and meaning negotiation. A major feature of learner interactions in this chat-based tandem learning was expert assistance, which was bilateral and reciprocal between the paired learners. Data analysis reveals that the learners in this study actively provided a variety of assistance for their partners along with high levels of responsiveness to the linguistic problems or difficulties their partners were undergoing, and both learners supported each other in their foreign language learning by alternating the roles of expert and novice. In the process of providing and receiving peer assistance, the tandem learners employed various types of strategies for achieving intersubjectivity, through which the expert and the novice learner arrived at mutual understanding. Meaning negotiation was found as a dialogic strategy for achieving and maintaining intersubjectivity through which the learners provide and receive appropriate assistance in their language learning conversation. The findings also indicate that even in the absence of meaning negotiation, learners focus on form and modify their language through the process of providing and receiving peer assistance. This study thus suggests that expert assistance rather than meaning negotiation may facilitate foreign language learning, which challenges the claim that meaning negotiation may be the only part of interaction which promotes L2 acquisition. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]