This paper dissects citation studies concerning features of citations per se and those studies of citation use across disciplines, cultures and developmental stages, which are followed by an outlook for future studies of citations based on research gap from the aspects of research contents, theoretical foundations and research methods. The results indicate that related studies pay special attention to the use of citations by expert writers and native English writers drawing on data from self-built corpus and interviews. Moreover, these studies are carried out from the interpersonal perspective, with a focus on both the categorization and the evaluative value of citations. Therefore, future studies should differentiate citation practice of learners at various levels, and make further efforts both on the automatic retrieval of and cognitive reflection on corpus data, and on expanding the depth and breadth of their theoretical foundations.