This paper surveys current linguistic research into early English-Celtic contacts and discusses some of the approaches and methods employed. In the first half of the paper, I explain why it is crucial to understand the sociolinguistic situation in Anglo-Saxon England when evaluating Mediaeval English data. I also show how the contrastive method and linguistic typology can be used to identify possible instances of Celtic influence on English in the first place. In the second half of the paper, I present case studies of possible Celtic phonological influence on English. In each instance, dialectal, place-name, metrical, and typological evidence are brought to bear on the particular development in order to reach firmer conclusions.