Numerous studies have examined the processing of inflectional morphology by second language learners, with the underlying aim of determining whether native-like processing can ever be attained. Indeed, this is an area where L2 speakers show notorious deficits, in contrast to the achievement of “target-like” grammar in other areas. The present paper reviews a series of experiments performed using online measures, notably ERPs and the recording of eye-movements, to address this question. The novelty of the present work lies in its emphasis on the properties of the L2 itself, i.e., “input factors” and how they may affect learning rate.