As part of a larger project, this study explores Vietnamese college students' use and concepts of cohesive devices in writing. Cohesion is a crucial element that ties components of a text together. Although the use of cohesive devices in L2 writing has been investigated by a large body of research, there is no such study exploring the effects of L2 learners' misconceptions of this word class. One hundred sixty-eight academic reports of totally 67,400 words written by Vietnamese final-year English-majored undergraduate students were collected for data analysis. An email invitation was sent, and 23 students accepted to participate in semi-structured interviews which were audio-recorded for analysis. The findings showed that the students employed references, conjunctions, and lexical items the most frequently in writing. Interestingly, the students' cohesion use and errors had similar patterns. The transcript analysis showed that the students' misconceptions of some language items and writing requirements affected their choice of cohesive devices. The current study gives implications for teaching and learning of this word class in L2 contexts.