Do you prefer coursebooks, courses, personal tutors? Or are you more tech-savvy and use apps on your smartphone? In any case, check out this interesting presentation on the origins of Duolingo by one of its founders, Luis von Ahn.

What’s in the air you breathe? - Amy Hrdina and Jesse Kroll

https://ed.ted.com/lessons/what-s-in-the-air-you-breathe-amy-hrdina-and-jesse-kroll

What does it mean to be a refugee? - Benedetta Berti and Evelien Borgman

https://ed.ted.com/lessons/what-does-it-mean-to-be-a-refugee-benedetta-berti-and-evelien-borgman