In this study, we examined the effect of previewing unfamiliar vocabulary on the real-time reading behavior of first language (L1) and second language (L2) readers. University students with English as their L1 or L2 read passages with embedded pseudowords. In a within-participant manipulation, definitions of the pseudowords were either previewed before reading or reviewed after reading. Previewing significantly affected reading behavior on early and late eye-movement measures, and the patterns of change on the first three contextual encounters with the pseudowords differed for L1 and L2 readers. On the multiple-choice cloze posttest, encountering novel words in reading followed by definitions resulted in somewhat more accurate responses for L1 but not L2 participants. The learning condition did not affect the results of the meaning recall posttest. These findings contribute to a more nuanced understanding of the relationship between vocabulary support approaches and the reading behavior of L1 and L2 readers when they encounter unfamiliar words in texts.