It is widely agreed that much second language vocabulary learning occurs incidentally while
the learner is engaged in extensive reading. After a decade of intensive research, however, the
incidental learning of vocabulary is still not fully understood, and many questions remain
unsettled. Key unresolved issues include the actual mechanism of incidental acquisition, the type
and size of vocabulary
... [Show full abstract] needed for accurate guessing, the degree of exposure to a word needed for
successful acquisition, the efficacy of different word-guessing strategies, the value of teaching
explicit guessing strategies, the influence of different kinds of reading texts, the effects of input
modification, and, more generally, the problems with incidental learning. This article briefly
surveys the empirical research that has been done on these issues in recent years.