IMSLP:Verifying copyright status

If you want to submit re-engraved (re-typeset) scores, please also see the permissible licenses page. This refers mainly to new editions of public domain works.
For copyrighted new works, see Creative Commons and Performance Restricted licenses. This includes new compositions, and new arrangements of public domain works.

For a simple description of copyright and the public domain, see IMSLP:Copyright Made Simple. For a more detailed description, see: Public domain. Questions may be directed to the forums. The following is meant to serve as a simplified guide on how to determine whether or not something is in the public domain, but please check public domain for details.

How to verify if your copy is in public domain

You should do some basic research if you are planning to upload a score that is not yet identified as public domain.

You should first determine the year of death for the composer and for any other person who was involved in the creation of the work in question. This would include arrangers, editors, authors of original texts and translators.
Works of composers, arrangers and text authors who died in 1972 or later are not eligible for uploading to the main server (in Canada).
The work of an editor who died in 1972 or later may or may not be allowed. The editing is of a of a work. In addition, to be allowed under site rules, the edition in question would have to be published over 25 years ago or be in the public domain in Germany.
A work first published in 1928 or earlier will be in the public domain in the United States even if contributors died too recently for it to be in the public domain in Canada. Additionally, a work published between 1929 and 1963 may be in the public domain in the United States due to non-renewal in some cases. Please see public domain for details. Any work that is in the public domain in the United States can be uploaded to Petrucci Music Libary US by following the upload instructions.
It is always important to find the year (and, preferably, place) of first publication and/or performance, if possible, especially for any composer who died after 1949.
On most scores, the year in which the score is copyrighted is printed on the first page of music. Notices also appear on the title page, the title page verso (back side), or even a contents or instrumentation page. However, many European scores from the 1800s all the way up through the 1980s bear no copyright notice. Absence of a copyright notice is no longer a guarantee that a given work is public domain in the USA (or elsewhere)!
You can look up date ranges for publishers, locations, and other helpful information (plate number styles) on the Historical Publication Info page, or the pages devoted to specific publishers that are linked there, like Breitkopf und Härtel.
There are some ways to estimate the publication date. One is to identify the editor of the score, whose name typically appears on the first page of music and/or title page, and google or wiki them to determine whether they are in public domain yet. There are also bibliographies of specific composers that give extensive info on dates of first publication and reissues, the original publisher, successor publishers, addresses, retail prices, plate numbers, engravers, and printers. James J. Fuld's The Book of World Famous Music is particularly rich in such information. Lastly, you could look up the publisher's information either via the web or printed catalogs. Some publishing companies were defunct before 1929 (which would be indicative of US public domain status). Others keep a database with old publications on their website.
Look up the publisher's information in library catalogs. Many libraries keep publication information like dates, plate numbers, editors in their database.

Juilliard On-Line Catalog has a fairly comprehensive database with plate and edition numbers.

Indiana University keeps plate and edition numbers for some works.

Worldcat does not always list full bibliographic information, but many publications are in Worldcat. Some plate numbers seem to be in a 'concealed' way in their database; entering a plate number in the search function will very often give the right hits.

The back covers of old scores often contain valuable information, such as a list of publications by the same publisher in print at the time the piece you've scanned was first issued!
Try a search on Google / Google Scholar with the title of your edition. Often, new editions were reviewed in musical periodicals. If you have access to jstor.org (which you may have through a library or university), you will find useful periodicals.
Sheetmusicplus lets you have a look at the first pages of a score. This is very valuable as you can find edition numbers and plate numbers here in some instances — there are many public domain items available on that site.
Google books include many reprints (e.g., from Dover and Kalmus) with sample pages available. While there are a fair number of public domain scores available at Google books, they are all marked with the Google logo and include metatags. All logos and metatags should be removed before uploading to IMSLP (preferably while also converting the best available scan images to monochrome in most cases).
Musicsack (now offline; check the Internet Archive) is a good resource in researching music-related people information.
See the public domain page for information on how to find US renewal registration and when this is and is not required.
When you've finished your research, please add the results of your work to one of the pages above to make it easier for other users, and also add information to the file description form to prove that your copy is in the public domain.

Avoid reproducing trademarks and logos

With the relatively recent advent of scanned music, a number of commercial enterprises have been formed to sell scans of public domain works. The three major companies doing this are CD Sheet Music, Everynote, and Elibron. While the content of the scores produced by these three concerns is public domain, any added original material such as prefaces is protected by copyright, and thus must be removed. In order to increase direct reusability (and in the interest of quality), all logos, added prefaces, and added metatags should be removed if possible before uploading such scores to IMSLP.