Creating an ebook in EPUB format is easy, for certain values of "easy". All one really needs is a text editor, a few command-line utilities; also needed is a working knowledge of XHTML, CSS, along with an understanding of the format's structure and required boilerplate. Creating a well-formatted and attractive ebook is a bit harder. However, it can be made easier with an application custom-made for the purpose. Sigil is an EPUB editor that provides the tooling authors and publishers may be looking for.