A copyright troll is a party (person or company) that enforces copyrights it owns for purposes of making money through litigation, in a manner considered unduly aggressive or opportunistic, generally without producing or licensing the works it owns for paid distribution. Critics object to the activity because they believe it does not encourage the production of creative works, but instead makes money through the inequities and unintended consequences of high statutory damages provisions in copyright laws intended to encourage creation of such works. 

Both the term and the concept of a copyright troll began to appear in the mid-2000s. It derives from the pejorative "patent trolls", which are companies that enforce patent rights to earn money from companies that are selling products, without having products of their own for sale. It is distinguished from organizations such as ASCAP, which collect royalties and enforce copyrights of their members. 

Limitations and exceptions to copyright are provisions, in local copyright law or Berne Convention, which allow for copyrighted works to be used without a license from the copyright owner.

Limitations and exceptions to copyright relate to a number of important considerations such as market failure, freedom of speech, education and equality of access (such as by the visually impaired). Some view limitations and exceptions as "user rights"—seeing user rights as providing an essential balance to the rights of the copyright owners. There is no consensus among copyright experts as to whether user rights are rights or simply limitations on copyright. See for example the National Research Council's Digital Agenda Report, note 1. The concept of user rights has also been recognized by courts, including the Canadian Supreme Court in CCH Canadian Ltd v. Law Society of Upper Canada (2004), which classed "fair dealing" as such a user right. These kinds of disagreements in philosophy are quite common in the philosophy of copyright, where debates about jurisprudential reasoning tend to act as proxies for more substantial disagreements about good policy.

The idea–expression distinction or idea–expression dichotomy is a legal doctrine in the United States that limits the scope of copyright protection by differentiating an idea from the expression or manifestation of that idea. 

Unlike patents, which may confer proprietary rights in relation to general ideas and concepts per se when construed as methods, copyrights cannot confer such rights. An adventure novel provides an illustration of the concept. Copyright may subsist in the work as a whole, in the particular story or characters involved, or in any artwork contained in the book, but generally not in the idea or genre of the story. Copyright, therefore, may not subsist in the idea of a man venturing out on a quest, but may subsist in a particular story that follows that pattern. Similarly, if the methods or processes described in a work are patentable, they may be the subject of various patent claims, which may or may not be broad enough to cover other methods or processes based on the same idea. Arthur C. Clarke, for example, sufficiently described the concept of a communications satellite (a geostationary satellite used as a telecommunications relay) in a 1945 paper that it was not considered patentable in 1954 when it was developed at Bell Labs.