Let’s say you’re cheerfully writing an article, and you realize that you’ve already written about the exact same situation. You pull up the old document, cut and paste the salient bits, and voila! You’re on to writing the next section, and you’ve just plagiarized yourself. The good news is that if you wrote about it and didn’t publish it or accept any money for writing it, you can use it. The bad news is that if you did publish it or accept money for it, you don’t own it anymore. It’s kind of like fixing up an old car and selling it. Once you’ve sold it, you can’t just take it for a spin if you need a car. Yes, you did all the work, but you sold it and it isn’t yours anymore. Anything you wrote for an employer or under contract is wholly owned by that employer, even if it was your devilishly clever idea and implementation. They paid you to have clever ideas and implement them, and they get to keep your work and do with it as they will. You only get to point to it with pride and pat your wallet. You also can’t take the publisher’s verbal okay to re-use all or part of that earlier document. If the second publisher decides to sue for your fee or not to pay you because the material wasn’t original to the new document, you won’t have a legal leg to stand on. You need to get permission in writing that it’s okay to re- use text, and even an email will do. If you don’t get permission, you’ll get a bad reputation at two publishers, because you didn’t take the time to write a new piece or the few minutes it takes to get permission. Audiences for technical subjects tend to read everything that’s published on the subject. That means that they already read that other piece and you don’t want to diminish its importance by using the same old stuff again. You also don’t want to publish something on your own website and then turn around and sell it to some other publication for the same reason. You’ll lose your audience. People will stop reading your work and publishers will stop hiring you. Surely you have something new to offer? Using other people’s work is more complicated. Of course you know that you can’t just copy someone’s work verbatim, put your name on it, and turn it in. But you CAN quote from someone else’s work, and as long as you properly attribute it, you can quote up to 10% of a printed page without getting permission (this is called “fair usage”). The attribution needs to be right there where the copied text is, or asterisked and footnoted. You can’t just thank someone at the end, knowing that they will recognize their own work. By the way, 10% of a printed page is about 30 words. If you’re going to use more than that, you need to get permission. If you do a lot of quoting, people will stop hiring you to write things and just go to the source. Code is much trickier than plain old text regarding permissions. Obviously, you need to attribute borrowed code, and make note of any deviations you made to customize the code for your purpose. But the original author may have sold the rights to the code, or distributed them with caveats, and you need to check those out and comply. That’s for all of the code, not just 10%. Because code has a function other than conveying information, you have to be more meticulous than with text alone. Otherwise it’s like putting a Ferrari exterior on your ’68 beetle engine and selling it as a Ferrari. Your client is going to be hopping mad when they put it in gear. I have a theory about why there’s so much plagiarism in technical writing. When you’re in school and you write a paper, it’s fair game to absorb the ideas of other writers and repeat them in your own words so long as there’s a bibliography at the end. That’s perfectly legal and expected. But a major difference between writing a paper for school and writing one for publication is copyright. The academic stuff you wrote is copyrighted to you by default and stays yours unless you sell it. (The law says that you own it from the moment of writing it down, unless you were under contract to write it, and until it is published, when the publishing entity, by default, owns it unless otherwise specified.) It works out like keeping a journal: as long it isn’t disseminated, you can quote and copy to your heart’s content. But if it’s disseminated, even if only a little bit, you need to play by the rules.