This chapter reviews research about the collaborative use of concept maps for learning. Although decades of research have produced some understanding of the cognitive effects of using concept maps in individual learning, theories about their effects in collaborative learning are less firmly established. The review incorporated a systematic literature search, analysis of dependent variables as effect sizes, and discussion of representative studies. Students who learned collaboratively by constructing concept maps outperformed those who learned from other activities such as studying texts, outlines, lists and lectures. However, no effect of studying pre-constructed concept maps in collaborative settings was statistically detected. There was homogeneity across the subsets of studies investigated. The review concludes with suggestions for future research in learning with concept maps in collaborative environments.