This article presents a selective overview of studies that have investigated auditory language processing in children and late second-language (L2) learners using online methods such as event-related potentials (ERPs), eye-movement monitoring, or the cross-modal priming paradigm. Two grammatical phenomena are examined in detail, children's and adults' processing of German plural inflections (Lück et al. Brain Res 1077:144–152, 2006; Hahne et al. J Cognitive Neurosci 18:121–134, 2006; Clahsen et al. J Child Language 34:601–622, 2007) and language learners' processing of filler-gap dependencies in English (Felser C, Roberts L Second Language Res 23:9–36, 2007; Roberts et al. J Psycholinguist Res 36:175–188, 2007). The results from these studies reveal clear differences between native and nonnative processing in both domains of grammar, suggesting that nonnative listeners rely less on grammatical parsing routines during processing than either child or adult native listeners. We also argue that factors such as slower processing speed or cognitive resource limitations only provide a partial account of our findings.