Q: Does "Under Review" mean the paper has been assigned to an external reviewer?

For most journals, the status "under review" is used to indicate that the paper has cleared the editorial check and has been sent for external review. However, status descriptions vary across journals, and some journals also use the status "under review" when the manuscript is under the initial editorial screening or review, and use "reviewers assigned" or "reviewers invited" to indicate that your paper has been assigned to external peer reviewers. You can check the journal's website to see if the statuses they use have been mentioned. If there has been no indication of reviewers being assigned, you will have to wait and see what the next status is to get a clearer view. If there is no change for more than a few weeks, politely write to the journal editor asking about the status of your submission.

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How long will the status of my paper show "Under Review?"

How long does it take for the status to change from "reviewers assigned" to "under review"?