"Interchange is a four-level, American English course that has been used by over 50 million students worldwide. This Intro Level Student's Book with Digital Pack has 16 units, four progress checks, and a Grammar Plus section to ensure students receive all the practice they need. Inside each book is a single-use code for the Digital Pack to access the Digital Workbook with hundreds of self-graded exercises, audio, videos, and an eBook. The Digital Pack is mobile-friendly and can be used on a smartphone, tablet, or computer."