I bought this bag to commute to and from the high school where I teach science. I wanted something that would be large enough to books, binders, class assignments, etc. I went with the medium based on the measurements on the website and I couldn't be happier. The medium size can hold a terrifying amount of stuff, yet sits comfortably across your back. The bag itself is high quality throughout. The vinyl lining is very stiff when new; it softens up with use. I like the simplicity of the bag, which contributes to its overall functionality and ease of use. I get the sense this may be the last messenger bag I ever have to buy.