A preprint is a complete scientific manuscript that has been posted to a public online server before it has been formally peer reviewed or published in a journal. It’s freely accessible to anyone, typically posted within a day of submission, and serves as a way for researchers to share their findings with the world quickly rather than waiting months (or years) for the traditional publishing process to play out.
How Preprints Fit Into Scientific Publishing
In traditional academic publishing, a researcher finishes a study, writes up the results, and submits the manuscript to a journal. The journal then sends it to other experts in the field who evaluate the methods, data, and conclusions. This peer review process can take anywhere from a few weeks to well over a year. Only after revisions and approval does the paper become publicly available.
A preprint skips that waiting period. The author uploads the finished manuscript to a preprint server, and it goes live almost immediately. The paper still gets basic screening for plagiarism and offensive or dangerous content, but no one evaluates whether the science itself is sound before it’s posted. The expectation is that a preprint is an interim step. The authors still intend to submit the work to a peer-reviewed journal, but they want the findings out in the open while that slower process unfolds.
Where Preprints Are Posted
Different scientific fields have their own dedicated preprint servers. The oldest and largest is arXiv (pronounced “archive”), which launched in 1991 at Los Alamos National Laboratory. It was originally built for physicists but has since expanded to cover mathematics, computer science, economics, and statistics. It now hosts over 1.8 million papers.
Biology researchers use bioRxiv, run by Cold Spring Harbor Laboratory. Medical and clinical researchers use medRxiv. Social scientists have options like SocArXiv and the Social Science Open Access Repository. There are also servers for psychology, neuroscience, and linguistics (CogPrints), and for humanities and social sciences through SAGE’s Advance platform. No matter the field, the basic model is the same: free upload, free access, no paywall.
What Screening Preprints Actually Get
Preprint servers are not a free-for-all, but the bar for posting is very different from journal publication. A 2020 analysis of preprint server policies found that 82% of servers screened submissions before or after making them public. About 68% screened before posting. Two servers used formal checklists, with one even issuing a badge for passed checks. But across the board, servers provided little explicit guidance on transparency in reporting or research integrity. The screening catches obvious problems like plagiarism or content that could cause harm. It does not catch flawed study designs, statistical errors, or unsupported conclusions.
How Preprints Compare to Published Papers
The good news is that the core findings of preprints tend to hold up. A scoping review comparing health-related preprints to their later peer-reviewed versions found that the general content and conclusions remained largely unchanged after publication. The science itself doesn’t usually shift dramatically.
What does change is the quality of the reporting around that science. Peer-reviewed versions were more likely to disclose funding sources, conflicts of interest, ethical approval, and study limitations. Disclosure rates for funding and conflicts of interest each improved by about 13 percentage points after peer review. Adherence to standardized reporting guidelines was also higher in published versions (a median of 42% compared to 33% for preprints).
One particularly telling difference involves “spin,” the practice of framing results in a more favorable light than the data supports. Among preprints studied, 65% contained spin, compared to 41% of their peer-reviewed counterparts. Peer review doesn’t eliminate spin, but it does reduce it significantly. This matters because spin can mislead readers into thinking a treatment works better than it does, or that a risk is smaller than the evidence suggests.
Why Preprints Exist
Speed is the primary advantage. Traditional journal publication can take six months to two years from submission to a paper appearing online. During that time, other researchers can’t build on the findings, check them, or apply them. Preprints eliminate that delay entirely.
They also remove the cost barrier. Most journal articles sit behind paywalls, accessible only to people at universities or institutions that pay for subscriptions. Preprints are free to read by anyone. When arXiv launched in 1991, its explicit goal was to level the global research playing field by giving everyone equal access to the latest results, regardless of institutional affiliation.
For researchers, preprints also serve as a timestamp. Posting a manuscript publicly establishes that you had a finding first, which matters in competitive fields where multiple labs may be working on the same problem. This has driven adoption in fast-moving areas. The machine learning community adopted arXiv in a major wave around 2015, and the pattern holds across disciplines: once a field starts using preprints for rapid sharing, it doesn’t stop.
The COVID-19 Surge
The pandemic transformed preprints from a niche academic practice into something the general public encountered regularly. Submissions to medRxiv increased tenfold between January and May 2020. COVID-19 preprints peaked at over 4,000 per month in May 2020. During the 2020 to 2022 period, COVID-related papers made up 3.5% of the roughly 12.5 million English-language journal articles and 5.3% of the nearly 1.3 million preprints published.
This surge highlighted both the power and the danger of preprints. On one hand, the scientific community could share and scrutinize findings about a new virus in near real time, accelerating the development of vaccines and treatments. On the other hand, unvetted studies about treatments, transmission, and origins circulated widely on social media, sometimes reaching millions of people before anyone had checked the work. The pandemic made “preprint” a word that news audiences had to learn quickly, often without the context to evaluate what it meant.
Do Journals Accept Papers That Were Preprints?
Most major publishers now accept manuscripts that were previously posted as preprints. Nature Portfolio’s policy is explicit: posting a preprint is not considered prior publication and will not affect whether a journal considers the paper. This represents a shift from a long-standing norm in scientific publishing called the Ingelfinger Rule, named after a New England Journal of Medicine editor who established it in 1969. The rule holds that journals require findings not to have appeared elsewhere before publication. Over time, exceptions have expanded to include conference presentations, public health announcements, and now preprints.
Nature does ask authors to disclose that a preprint exists when they submit to a journal, and to update the preprint record with a link to the final published version once it’s out. They also advise researchers who are contacted by reporters about a preprint to make clear that the work hasn’t been peer reviewed yet, that findings are provisional, and that conclusions could change.
How to Read a Preprint Critically
If you encounter a preprint, the most important thing to recognize is what it is and what it isn’t. It’s a finished manuscript that the authors believe is ready to share, but it has not been evaluated by independent experts. The conclusions might be solid, or they might change substantially once reviewers point out problems with the methods or analysis.
Look for a few things. Does the preprint clearly state its funding sources and any conflicts of interest? Does it acknowledge limitations? Is the sample size large enough to support the claims being made? If a news article cites a preprint, it should say so explicitly. If it doesn’t mention whether the study was peer reviewed, that’s a reason to dig deeper before sharing the findings or making decisions based on them.
Preprints are a valuable part of how science moves forward. They get information out faster and make it available to everyone. But they’re a first draft of the public record, not the final word.