The Introduction is the section most authors write first and revise most. It is also the section most responsible for desk rejection—not because it is poorly written, but because it fails to make the case that the study needed to exist. Understanding how to write an introduction is what separates papers that get accepted from those that don’t.

Editors and reviewers form their initial assessment of a paper within the first two minutes of reading. That assessment is based almost entirely on the Introduction. A paper that signals a clear gap, a specific question, and a compelling reason to answer it will be read differently—and more generously—than one that begins with generic background and arrives at the study objective as an afterthought.

Understanding what a strong Introduction is actually doing—the logic behind the structure—matters more than following any particular template. The template is the output. The logic is what produces it.

What the Introduction Is Trying to Do

The Introduction has one job: to make the reader believe that this study needed to be done.

Not that the topic is important. Not that the field is interesting. Not that prior studies exist. The specific study described in this paper needed to be done, and the Introduction is the argument for why.

This argument requires three moves, in order:
1. Establish what is known and why it matters
2. Identify what is not known, and why that absence has consequences
3. State what this study does to address the gap

Every strong Introduction makes these three moves. Every weak Introduction fails to make at least one of them completely.

Move 1: Establish the Clinical Context

The opening of the Introduction establishes the territory. It tells the reader: this is the clinical or scientific area we are entering, and here is why it matters to the audience of this journal.

This is not a literature review. It is a positioning statement. The goal is to activate the reader’s existing knowledge and orient them toward the specific problem the paper addresses.

Common mistakes in Move 1:

Starting too broad. “Cancer is one of the leading causes of mortality worldwide” is true and irrelevant to a paper about anastomotic leak in esophageal repair. The opening should establish the specific clinical territory, not the continent it is located in.

Starting with epidemiology for its own sake. Incidence statistics are useful when they establish the scale of the problem being addressed. They are not useful as a way to fill space before getting to the point. If the incidence data does not directly support the case for why the gap matters, it does not belong in the opening.

Summarizing the entire history of the field. The Introduction is not a textbook chapter. It needs enough background for the reader to understand why the gap exists—not a comprehensive account of how the field developed.

A well-executed Move 1 is two to four sentences that establish: what the clinical problem is, who it affects, and what the current standard of knowledge or practice is. Everything else is setup for Move 2.

Move 2: Identify the Gap

The gap statement is the most important sentence in the Introduction. It is the direct justification for the study’s existence.

A gap is not simply the absence of a prior study. A gap is an absence of evidence for something that matters clinically or scientifically. The two requirements—absence of evidence, and mattering—must both be present.

Absence without consequence is not a gap. “The specific timing of suture placement in neonatal bowel anastomosis has not been studied” may be true. It is not a gap unless there is a reason to believe timing affects outcomes. The gap statement must connect the missing evidence to a clinical or scientific consequence.

Contradiction is also a gap. When existing studies produce conflicting results, the gap is the unresolved contradiction. The Introduction should characterize the disagreement specifically—which studies showed what, and why the contradiction matters—rather than vaguely noting that “results are inconsistent.”

Limitation of existing evidence is a gap. If all existing data comes from single-center retrospective series, the gap is the absence of prospective or multicenter data. If all existing studies used a surrogate endpoint, the gap may be the absence of patient-reported outcome data. The gap should be stated in terms of what type of evidence is missing, not just that studies are absent.

The gap statement is typically one to two sentences. It should be specific enough that the study objective in Move 3 follows directly from it. If the objective does not follow directly from the gap, either the gap statement is wrong or the study is not addressing the right question.

Move 3: State the Objective

The objective statement closes the Introduction by naming what this study did to address the gap.

It should be one to two sentences, structured as an action: “We conducted a prospective cohort study to evaluate X in Y population with Z outcome.” The verb matters—evaluated, compared, assessed, examined—because it specifies the type of inference the study makes.

The objective statement is not a restatement of the gap. The gap is what was missing. The objective is what was done about it. “Therefore, this study aimed to investigate the relationship between X and Y” is a weak objective because it restates the topic without specifying the design, population, or outcome.

A strong objective statement allows a reader to predict, from the Introduction alone, what the paper’s primary outcome table will look like. That level of specificity is the standard.

The Funnel Shape

The three moves produce the classic funnel structure: broad context narrowing to specific gap narrowing to precise objective.

This shape is not arbitrary. It follows the reader’s cognitive journey. The reader enters the Introduction with general knowledge of the field. Move 1 activates the relevant portion of that knowledge. Move 2 narrows attention to the specific problem. Move 3 focuses attention on this paper’s contribution to that problem.

A reader who reaches the objective statement having followed this funnel is prepared to evaluate whether the study design, described in the Methods, is adequate for addressing the gap. That preparation is what the Introduction is supposed to provide.

Introductions that do not follow this funnel disorient the reader. An Introduction that begins with the gap before establishing context asks the reader to evaluate the importance of a problem they have not yet been oriented to. An Introduction that presents the objective before identifying the gap asks the reader to accept the study’s rationale without being given the rationale. The funnel shape exists because it matches how understanding is built.

Length and Proportion

A short-form paper (under 3,000 words) should have an Introduction of 250–400 words. A full-length manuscript may reach 500–600 words. Beyond that, the Introduction is typically doing work that belongs elsewhere.

The proportion rule is: Move 1 should be the shortest section, Move 2 the longest, and Move 3 the most precise. The gap receives the most space because it requires the most justification—it is the claim that the study was necessary. Move 1 and Move 3 are positioning and conclusion; they require less text.

An Introduction that has more text in Move 1 than Move 2 has prioritized background over justification. This is the most common length problem in Introductions: too much context, too little gap analysis.

Writing the Introduction Last

The most practical advice about writing the Introduction is to write it last.

This is counterintuitive because it is the first section the reader encounters. But it is the section that depends most on knowing what the paper found and which aspects of the prior literature turned out to be most relevant to the findings.

An Introduction written before the analysis is complete is written for a study the author expected to run. After analysis, the study that was actually run may differ in emphasis, scope, or primary finding. The Introduction written first will need to be rewritten to match the paper that was produced.

Writing the Introduction last—after the Results and Discussion are drafted—allows the author to build Move 2 around the gap that the study actually filled, not the gap the author expected to fill. It allows Move 1 to be trimmed to exactly the background the reader needs to understand the Discussion’s interpretation. And it ensures that Move 3 matches the study that was run, not the study that was planned.

The workflow for drafting an Introduction using reverse outlining—starting from the Discussion and working backward—is the practical implementation of this principle.

Common Structural Failures

The literature review Introduction. Three or four paragraphs summarizing the existing research in chronological order, with the study objective appearing in the final paragraph. This structure fails because it presents information without making the argument for the gap. The reader knows what has been studied but not why the current study was necessary.

The methods preview Introduction. An Introduction that spends significant space describing the study design, inclusion criteria, or statistical approach before the reader has been given a reason to care about the study. Methods belong in the Methods section.

The overclaiming Introduction. An Introduction that describes the study as addressing a large, important clinical problem, when the study is a single-center retrospective series with a small sample. The mismatch between the scale of the claimed gap and the modesty of the study design is visible to reviewers and damages credibility.

The vague gap statement. “However, limited data exist on this topic” is a placeholder, not a gap statement. It does not specify what data is limited, why the limitation matters, or what would change if the data existed. Vague gap statements signal that the author has not thought carefully about why the study needed to be done.

For a related perspective, see What Editors Actually Mean by ‘Lack of Depth’.

The Practical Test

Before submitting, read only the Introduction and the Conclusions. The Conclusions should be a direct answer to the gap identified in the Introduction. If the Conclusions address a different question than the one the Introduction framed, either the Introduction was written for the wrong study or the Conclusions have drifted beyond what the study can support.

This test is fast and reliable. A paper that passes it—Introduction frames the gap, Conclusions answer the gap—has structural coherence that makes every other section easier to evaluate. A paper that fails it has a problem that cannot be fixed by revising sentences.

The Introduction is the argument that the study needed to exist. Everything that follows is the evidence for that argument. Getting the Introduction right is not a writing task—it is the work of being clear about why the study was worth doing.