This article discusses how research on language transfer in the field of SLA can help to explain the origins of substrate influence in creoles and provide answers to more difficult questions concerning the distribution and verification of substrate features. First, it argues against the view that both SLA and transfer are not involved in the genesis of pidgin and creole languages. Then the view is presented that, as described in the SLA literature, transfer is not just a consequence of second language learning but also of second language use, and it serves as a communication strategy when the need arises. Such a strategy may be used by speakers of either a prepidgin or an already established pidgin when its functional use is being rapidly extended. Sociolinguistic perspectives on transfer in SLA, described next, throw some light onto the question of why substrate features remain in pidgins and creoles. Research on transfer in SLA also provides important insights into the specific factors that may have affected substrate influence in creoles. Evidence is presented that some transfer constraints discovered in SLA research—rather than other proposed factors such as so-called functional expendability—still provide the best explanation for the absence of particular substrate features in creoles. Finally, it is shown that tests proposed for verifying instances of L1 influence in interlanguage could be adapted for verifying instances of substrate influence in creoles.