Is it legal to add your publications to ResearchGate? I recently created a profile on ResearchGate. And to add your publications list it requires you to upload the paper. Is it legal to upload published journal articles on public servers, where everyone can download it for free?
Is it legal to upload published journal articles on public servers, where everyone can download it for free?


It depends on the publishing agreement you signed, which should specify which rights the authors and the publisher hold.  The allocation of rights depends on the journal (and the field you are working in), and sometimes there are modifications or addenda for a specific paper.

You should keep copies of the publishing agreements for your papers, precisely so you can refer to them at times like this.  If you don't have them, you can get an approximation by looking on the journal's website to see what their current policies are.  The policies could have changed over time (and in principle the publisher could still enforce a stricter policy you agreed to in the past), but it's probably safe to post a paper online if the publisher allows it as part of the current publishing agreement.  If you're feeling nervous, you could always ask the publisher whether you could follow the terms of the current publishing agreement for your paper that was published long ago.