The Wikipedia website now includes tools to help you create formatted ebooks using content from one or more Wikipedia pages – here’s a sample ebook in the EPUB format.
Wikipedia has offered the PDF export functionality on their website for some time but with the recent change, you can export a selection of Wikipedia pages as EPUBs which is a much better format for reading articles offline on mobile phones, ebook readers and tablets. PDF is still a more suitable format for creating print-ready ebooks.