This chapter reviews current studies focusing on the production, comprehension, and processing of words and idiomatic expressions in neurotypical and neurodiverse Gaelic-speaking children and adults. The review of the literature highlights that the majority of studies on word learning have focused on primary school children attending Gaelic-medium education. This is not surprising given that the revitalisation of Gaelic is pursued through Gaelic-medium education (GME). The majority of new speakers, that is second language learners of Gaelic without prior cultural affiliation to Gaelic, are children or adults from non-Gaelic-speaking homes attending GME. The studies targeting lexical processing or asking how multiword expressions in the form of idioms are acquired highlight that many questions about Gaelic word learning and processing in the early years and across the lifespan are yet to be addressed. The chapter concludes by highlighting where the major research gaps are and by putting forward suggestions for future research.