Taking 1925, the founding year of "Language", the journal of the Linguistics Society of America, as a benchmark for "the past", and 2015 as benchmark for "the present", the author considers what was known then and what is known now about second language acquisition in applied linguistics. The field has grown more complex and interdisciplinary over the past 90 years, and developed in ways the founders could not have predicted. Because the essential mission of applied linguistics is to cross disciplinary and physical borders in the process of understanding and resolving language-related problems of all kinds, and because those problems are often unpredictable, the author concludes it would be foolhardy to try to predict the future of applied linguistics--particularly if applied linguists continue to do their jobs as "border-crossers".