THiNK is a series for secondary school students learning English as a second language. The series is published by Cambridge University Press and written by Herbert Puchta, Jeff Stranks and Peter Lewis-Jones. 

THiNK's thought-provoking topics and a focus on developing cognitive skills challenge and inspire teens to become lifelong learners.

There is also THiNK Quick for short courses. This is available for levels 2 to 4 (B1 to B2).