Incidental learning from guessing the meanings of words from context through listening and reading is the most important of all the sources of vocabulary learning. This is particularly true for native speakers learning their first language, but it should also be true for second language learners, but many do not experience the conditions that are needed for this kind of learning to occur. A major goal of this chapter is to look at these conditions and see how they can be established. We will look at how successful learners can be at guessing from context, how much and what kind of learning can occur from this guessing, and how learners can be helped to become skilful at guessing from context. The chapter includes a description of a guessing from context strategy which can be used for learner training. To become good at guessing from context, learners need to develop their reading skill, need to read material which as at the right level for them, and need to practice the guessing strategy.