A defensive publication, or defensive disclosure, is an intellectual property strategy used to prevent another party from obtaining a patent on a product, apparatus or method for instance. The strategy consists in disclosing an enabling description and/or drawing of the product, apparatus or method so that it enters the public domain and becomes prior art. Therefore, the defensive publication of perhaps otherwise patentable information may work to defeat the novelty of a subsequent patent application.
One reason why companies decide to use defensive publication over patents is cost. In the United States, for example, to obtain a published patent application, one must incur at least filing fee, examination fee, search fees, and early publication fees (currently $530, minimum plus $300 for early publication), and meet the filing requirements for a proper patent application.
- "The defensive publication route is especially useful for innovations that do not warrant the high costs incurred in patent applications but to which scientists do want to retain access." 
- Johnson, Justin P., Defensive Publishing by a Leading Firm (October 8, 2004). Available at SSRN: http://ssrn.com/abstract=606781 or doi:10.2139/ssrn.606781 (pdf[dead link]).
- Baker, Scott and Doug Lichtman and Claudio Mezzetti, Disclosure And Investment As Strategies In The Patent Race, University of Chicago Law School. 2000. (pdf)