Librarian and blogger Daniel Gustavsson has written a book about how and why to present comics in the library, and which comics that should be. The intended audience for the book is first of all librarians, but it is also suitable as an introduction to comics for, well, for just about anybody.
About half of it is theoretical, first introducing the comics medium to those who aren't used to reading comics, then presenting different comics genres and giving brief histories of the comics medium in the U.S., Europe and Asia (mainly Japan, of course), a bit on how to treat comics in the library (including about buying comics in foreign languages) and a couple of pages explaining various terms, especially terms dealing with Japanese comics genres. Not-quite half the book is recommendations for libraries on high-quality comics collections that would be suitable to buy (and not just for libraries but for aspiring comics aficionados as well), some good books about comics, and a couple of informative web sites.
Even though the already-knowledgeable comics reader can probably learn something from the theoretical parts and also get some tips on good comics they might not be aware of, it's as an easy-to-read, knowledgeable introduction to the comics medium this book shines. The writing is crisp and informative, and the what-to-read advice is generally good. Well worth reading for the Swedish-speakers out there who want/need to learn more about comics.
The rest of you, get Brian Walker's two-volume comics history instead. It's great, and it's coming out in a collected edition this year.