Internationally, an increasing number of children learn English as an Additional Language (EAL). Children with EAL grow up in an environment where English is the majority language, but are exposed to a different, minority language at home. Despite the increase in the number of EAL learners around the world, comparatively little is known about the development of their vocabulary and grammar at preschool age. Furthermore, the use of different methods in EAL studies can make research evidence difficult to summarise. The aim of this chapter is to provide a comprehensive review of EAL learners' vocabulary and grammar development at preschool, drawing from studies that have used standardised tests, experimental tasks, or both. This review indicates that few studies have focused on preschool children with EAL. These suggest that, at the earliest stages of language learning, EAL learners generally know fewer words and acquire grammatical constructions at a slower pace than their English monolingual peers. These differences often persist throughout development, risking a negative impact on EAL learners' academic attainment in an English-only school environment. Thus, this chapter also includes AUTHOR-PRODUCED COPY 2 some suggestions for practice that could help children with EAL develop their vocabulary and grammar knowledge during and after preschool.