A Wikipedia Book 

is an organized collection of Wikipedia articles that can be rendered electronically in PDF format, or ordered as a printed book. The book is compiled afresh each time it is downloaded or ordered, so will always reflect theversions of the articles.

Note: Currently (2015) not all information in an article will be displayed when rendered in book format - in particular, since 2014 information held in tables (including infoboxes) has not been displayed. Nor has maths markup