With the expansion of online language learning opportunities, language teachers and learners are presented with an increasingly diverse range of tools to facilitate language learning in various contexts. However, CALL researchers and practitioners often have limited knowledge about the effectiveness of online language learning primarily due to a lack of research on online language learning outcomes and on valid assessment measures. Despite the challenges in assessing language learning online, the editors of this volume believe the wide range of online language learning opportunities has brought new tools and methods to both strengthen assessment and inform pedagogical decisions in online language teaching. In terms of assessment, technology first provides researchers and practitioners with more options to document learners' language use in different contexts and their progress over time. The instances of learners' actual use of language will complement any achievement and proficiency measures of language learning outcomes. Moreover, the use of technology motivates researchers and practitioners to re-conceptualize assessment of online language learning. More importantly, technologies make it possible for the assessment to be incorporated for the purpose of learning (e.g., adaptive learning) and teaching (e.g., technology-mediated dynamic assessment and teacher intervention). Assessment Across Online Language Education examines these challenges emerged in online language teaching and learning, explores the new opportunities for language teachers and learners, and provides suggestions for future research on assessment and learning in online language education.