Peer feedback is widely used in second and foreign language writing contexts. While second language (L2) proficiency is likely to be an important factor in determining peers' ability to give and utilize feedback, its contribution has been relatively under-researched. In the present study, 54 undergraduates in a foreign language writing context gave and received feedback on two different texts. The quantity and type of feedback given and incorporated were analysed, looking at whether these changed or preserved meaning. Generalized linear mixed models were used to assess whether the L2 proficiency of the reviewer (reviewer proficiency) and writer (writer proficiency) in each dyad determined the quantity and type of feedback given and incorporated. Results showed that reviewer proficiency significantly predicted the number of suggestions made. Writer proficiency did not significantly predict the number of suggestions, though lower proficiency writers incorporated significantly fewer meaning-related suggestions into their revised texts than higher proficiency writers. Differences in giving and incorporating suggestions also emerged for different pairings (i.e. matched or mixed proficiency), though these were not significant. The present findings provide further insight into understanding how L2 proficiency modulates the peer feedback process.