APA (7th ed.) Citation

Harley, B. (1990). The Development of second language proficiency. Cambridge University Press. https://doi.org/10.1017/CBO9781139524568

Chicago Style (17th ed.) Citation

Harley, Birgit. The Development of Second Language Proficiency. Cambridge: Cambridge University Press, 1990. https://doi.org/10.1017/CBO9781139524568.

MLA (9th ed.) Citation

Harley, Birgit. The Development of Second Language Proficiency. Cambridge University Press, 1990. https://doi.org/10.1017/CBO9781139524568.