Ebooks come in a variety of different formats and each ebook reader has sligfhtly different specifications in terms of what formats it can read and display.

Perhaps the most well know format for ebooks is PDF from Adobe  and while the majority of ebook readers claim support for the format its not always the best suited to the smaller screen real estate offered by the majority of ebook readers and works better with computer screens.  A new emerging standard is EPub another adobe format specially created for the ebook market.  Other pertinent formats are AZW – the Amazon Kindle format, LIT – from Microsoft, BBeb – from Sony, and PNPd from Palm.  Of course there are hundreds of other formats out there like .DOC the format for word files which ebook readers will often read and .TXT the default text file format but how well each reader reads non native formats depends very much on the device, and the formatting of the book itself which could look great on one reader and awful on another.

Another important point to note is DRM.  Digital Rights Management, that pesky protection corporations use to lock down their books ostensibly so you cannot share your books over the Internet can be a real pain if your moving from one device to another, as DRM can be implemented (or not) on many of the common file types and can mean changing readers could mean your entire ebook collection will be of no use without some software conversion.