Reading research can answer the question of how to teach vocabulary to increase reading comprehension. Literature reviews show that almost any type of vocabulary instruction can produce significant gains in word knowledge, but that since more than this superficial knowledge is necessary to make a difference in reading comprehension, much vocabulary instruction fails. The definitional approach teaches labels rather than concepts, while the context approach is ineffective when taught as a discrete skill. Although combining these two teaching methods is effective, several new instructional techniques are still more "powerful." The characteristics of powerful techniques are integration, or establishment of connections or relationships between instructed words and other words and concepts; repetition, or repeated encounters with new words; and using word meanings to make inferences. Producing the largest vocabulary gains with limited instruction time also requires efficient as well as powerful instruction. Research suggests that most people learn vocabulary incidentally, from context, hence the following paradox: the most powerful method of vocabulary instruction is quite inefficient and the least powerful method is quite efficient. This leads to five recommendations for vocabulary instruction: (1) intensive instruction should be used for a relatively small number of carefully selected words, (2) powerful vocabulary instruction can be applied with intermediate levels of intensity to a large number of words, (3) the classroom atmosphere should be saturated with new and interesting words, (4) students should increase the time actually spent reading, and (5) students should be given instruction that will help them become more effective independent word learners. A four-page list of references is included. (HTH)