Online reading requires exquisitely precise co-ordination of the oculomotor processes involved in extracting and integrating information from both the word currently fixated in foveal vision and upcoming words in the parafovea. Parafoveal preview effects, assessed using the gaze-contingent boundary paradigm, provide a rich source of evidence about the extent and depth of processing conducted on upcoming parafoveal words and how it contributes to reading. This review focuses on recent demonstrations of plausibility preview effects which provide strong evidence that readers extract semantic information from parafoveal words, and that newly identified words are rapidly and incrementally integrated with the developing representation of the sentence to generate graded predictions about potential plausible continuations. Individual differences in the quality of skilled readers’ lexical representations, indexed by the combination of reading and spelling ability, determine how semantic and contextual information extracted from parafoveal words influences oculomotor control. This evidence has important implications for theories of eye movement control in online reading.