6. Krashen, S. (1988). Second Language Acquisition and Second Language Learning. Location: Prentice Hall
7. Krashen, S. (2004). The Power of Reading: Insights from the Research, 2nd Edition. Location: Libraries Unlimited
8. Krashen, S. (2011). Free Voluntary Reading. Location: Libraries Unlimited
9. Krashen, S. (2017). Comprehensible and Compelling: The Causes and Effects of Free Voluntary Reading. Location: Libraries Unlimited