Digital Right Management (DRM)  as applied to eBooks is generally a code that must be present in order for the reader to be able to open an eBook. The code may be locked to a particular device, or may be locked to a range of multiple devices. In other cases it is locked to a user. There is no standard implementation for DRM.
DRM is supposed to protect the author and publisher of eBooks (or eMusic and other electronic media) from pirating and other illegal activities. Some opponents call it Digital Restriction Management and claims it goes far beyond illegal activity and restricts items that are both legal and reasonable use.
Some eBook formats do not support DRM and even if a format supports it there may be eBooks in that format that are not controlled by DRM.
A given reading device may have multiple DRM schemes for the various formats it supports. Some formats, most notably MOBI have a restriction on dedicated reading devices that they will not permit their software to be used on a device that supports other formats using DRM.
DRM means Digital Rights Management and is both a mechanism and an idea. It generally intends to enforce a restriction on a user in what they can do with a particular file.
- Adobe ADEPT (EPUB/PDF)
- eReader (EPUB/eReader)
- TPZ or TOPAZ
- Wolf and MobiPocket or
- wikipedia:DMCA DMCA, Digital Millennium Copyright Act Wikipedia article
- wikipedia:Digital_Rights_Management Digital Right Management, Wikipedia DRM article
- Fictionwise free DRM testbook: "Around the world in 80 days" is a MOBI eBook that can be used to test the DRM feature of your eBook reader before actually purchasing any books.
- MobiRead Wiki is a knowledge base created by users of the MobileRead community.