Thanks to the trend of various changes in legislation, copyright terms can sometimes be cynically described as lasting at least X+20 years, where X is the number of years since the release of ''WesternAnimation/SteamboatWillie'', the first widely-released Mickey Mouse cartoon. It is generally believed, though inaccurately, that the most recent extension of American copyright duration — the [[https://en.wikipedia.org/wiki/Sonny_Bono_Copyright_Term_Extension_Act Sonny Bono Copyright Term Extension Act]] — was enacted at the behest of the {{Creator/Disney}} Company solely to keep Mickey Mouse cartoons from entering the public domain. This is why the act was derisively referred to by detractors as the Mickey Mouse Protection Act.[[note]]The ''real'' reason why it was enacted was that the EU harmonized its copyright laws, changing its standard term from life plus 50 to life plus 70, and equally significantly adopting a concept called the "rule of the shorter term". Under that rule, if two countries have different copyright terms, a work will be protected only for the shorter period in both countries. Without a US term extension to life plus 70, copyright owners would have been denied 20 years' worth of royalties in both the EU and US. There were also fears that failing to extend the US term would have hampered the commercial viability of genres that were more popular in Europe than the US, with jazz as one notable example.[[/note]]

Given Congress' willingness to extend copyright duration any time Hollywood demands it, it is entirely possible that -- in America at least -- the pool of public domain characters has reached its maximum size and will grow no larger, except by accident or oversight. As of January 2012, it is now possible in the United States for [[http://www.wired.com/threatlevel/2012/01/scotus-re-copyright-decision/ works to be taken back out of the public domain]], leading to the inevitable conclusion that the pool of public domain characters has not only reached its maximum size, it is likely to ''shrink''. (Ironically, the very same Hollywood corporations responsible for the original copyright durations would probably be the first to fight tooth and nail to ''keep'' certain properties in the public domain, if only so that they could continue making movies with some of the characters mentioned below.) However, no copyright extension took place in 2018—''not even Disney'' lobbied for such a change. In fact, the main US lobby for authors now publicly advocates ''reducing'' copyright terms![[note]]ItMakesSenseInContext... authors welcome new additions to the PD, allowing them to create works that would previously have been illegal.[[/note]] This means that for the first time in two decades, the public domain saw new additions in 2019, specifically (almost all) works created in 1923.[[note]]Sound recordings were not covered by US federal copyright law until February 15, 1972, with recordings fixed before that date protected only by state law. Pre-1972 recordings were later placed under the federal umbrella, but state law would not have been preempted until ''2067''. Finally, in 2018, state copyright laws were once and for all preempted with regard to pre-1972 sound recordings. Pre-1923 recordings entered the PD in 2022, with other pre-1972 recordings following in subsequent decades.[[/note]]

This reversal of extending copyrights can be traced to, at least for U.S. copyright laws, something that was just becoming part of everyday reality in 1998 when the Sonny Bono Act was passed: the Internet. With now almost any work of literature, TV, film, or music now available to download legally or illegally, trying to keep an iron grip on copyrighted works and characters has become near-pointless. To address this, many companies have set up streaming services and places to legally download works, usually with incentives in place to make it more appealing to the consumer like extras included before only found on [=DVDs=], higher picture quality for shows and movies, and offering a whole ''library'' of works on streaming services for a monthly rate instead of having to pay per download. Even Disney, the juggernaut that has often been responsible for copyright extension, has developed an "if you can't beat 'em, join 'em" attitude. They have now included many early cartoons for anyone to watch on their [=YouTube=] channel including, you guessed it, ''[[https://www.youtube.com/watch?v=BBgghnQF6E4 Steamboat Willie]]''.

A distinction should be made between public domain ''characters'' and public domain ''works''; WesternAnimation/BugsBunny is a still copyrighted character due to his first appearance "Hare-Um Scare-um" [[note]] Technically, he had two early shorts, "Porky's Hare Hunt" and "Prest-O Change-O", but he was unnamed at that time [[/note]] not being in the public domain yet, but some of his individual cartoons are. Those cartoons being in the public domain does not affect the underlining copyright of Bug Bunny's first appearance.[[note]] A case against George S. Brown by Disney showed that just because WesternAnimation/TheMadDoctor had it's copyright expired, it did not mean Mickey Mouse's copyright expired, due to Mickey Mouse's first appearance "Steamboat Willie" still being copyrighted at the time.[[/note]]

It should be mentioned as well the issue with derivative works, new works based on previous ones, such as adaptations. Although the ''original'' character or work may be in the public domain, a modern derivative work may not be. You can make your own derivative work of that public domain character, as long as it is clearly different from the version from the recent Hollywood blockbuster. Myth/NorseMythology, in and of itself, is in the public domain, but if you try to make a blond Thor with a red cape and a hammer that OnlyTheChosenMayWield,[[note]]In the myths, it's simply a hammer so heavy that only Thor, the strongest god of all, is able to lift. Stan Lee changed that part because it would be meaningless in a world filled with superheroes and supervillains with super strength[[/note]] you may be in trouble.

It should be noted that, in general, a {{MediaNotes/trademark}} is forever. As long as the holder of the trademark is creating some kind of "product" (media counts), and they fulfill certain requirements (protecting the trademark is generally required), they can demand that the courts enforce the trademark. This is another reason why trademarks have become more common.

One interesting side note to keep in mind is that there is a difference between ''copyright'' (the legal right to control the reproduction of a particular expression of an idea or concept) and ''trademark'' (a symbol, character, or design which is intended to be emblematic of a particular product or organization and used to identify them in a kind of visual shorthand). Public domain generally deals with copyright alone -- meaning that it might be possible for someone to legally write a story with a public domain character, only to find they cannot legally sell their story using that character's name because someone else holds the trademark. This ''has'' happened.

In the USA, the Supreme Court decision [[https://en.wikipedia.org/wiki/Dastar_v._Twentieth_Century_Fox Dastar v. Twentieth Century Fox (2003)]] ruled that a public domain work doesn't violate the trademark of the underlying work. The specific ruling was narrow and dealt with "reverse passing off", rather than using a trademarked name. The ruling is generally believed to apply to using names as well, in which case it would indeed be legal to use a trademarked name on a public domain story, but no case that confirms this has reached the Supreme Court yet.

Of course, even if a character isn't in the Public Domain, a good writer can [[WritingAroundTrademarks probably find a way]] to get that character in by creating a CaptainErsatz or an AlternateCompanyEquivalent, or by utilizing a LawyerFriendlyCameo. And if that writer can't even use ''a character he created'' thanks to the wonders of modern copyright law, then he can use an {{Expy}}. Sometimes, they can just graft that character onto a HistoricalDomainCharacter (see below). Of course, sometimes all this can just go too far when a certain popular character becomes known as a FountainOfExpies.

A character can also fall into the public domain if it doesn't meet the threshold of originality -- which means characters that are too simple to be copyrighted. For example, a single grey square cannot be copyrighted, nor can a stick figure.