The History of the Underline: From Medieval Manuscripts to Unicode

The underline is the simplest mark in writing: just a horizontal line beneath a word or phrase. And yet, in its long history, it has meant emphasis, importance, hierarchy, hyperlinks, error, sarcasm, and more — sometimes several things at once.

This post traces the underline from its earliest known appearances in medieval manuscripts, through the typewriter era when it became indispensable, to the modern web where it became inseparable from the hyperlink, and finally to today, where Unicode lets us underline almost anywhere we type.

It's a small mark with a surprisingly long story.

Before underlines: how scribes emphasized text

In the centuries before printing, scribes copying religious and academic texts had only a few tools for emphasis. They couldn't bold a word — letters were drawn one at a time with a quill, and there was no concept of switching between regular and bold styles mid-sentence. Italics didn't exist yet either. Color (especially red ink, called rubrication) was the most common way to highlight headings, important names, or the start of a new section.

Marginalia — notes drawn in the margins — was another form of emphasis, but more for commentary than for highlighting words within a sentence.

Underlining, when it appeared at all in early manuscripts, was usually pragmatic rather than decorative: a scribe might underline a word they wanted the reader's eye to find quickly, or mark a passage for later revision.

Medieval and Renaissance underlines

By the 13th and 14th centuries, underlining shows up more consistently in academic manuscripts, especially in commentaries on religious texts and legal documents. The function was specific: underlines marked proper names, biblical references, or the original passage being commented on — distinguishing it from the scholar's notes around it.

This is the underline's first stable meaning: here is the source text, distinguished from the surrounding analysis.

Renaissance printers inherited this convention. When the printing press arrived in the mid-15th century, early printed books continued underlining proper names and quotations for the same reason scribes had — to anchor important text visually in long passages.

But here's where things got interesting: print introduced italics (around 1500, designed by Aldus Manutius in Venice). Italics were faster to print than underlining (which required a separate manual mark) and looked more elegant. So italics gradually replaced underlines for the meanings they had carried.

By 1700, underlining in print had largely faded. It survived in handwritten manuscripts and personal annotations, where italics weren't an option.

The typewriter era: the underline returns

The typewriter, invented in the 1860s and mass-produced from the 1870s onward, brought the underline roaring back.

Why? Because typewriters had no italic key. They had a fixed set of letterforms — usually one font, no styles. If you wanted to emphasize a word, italics weren't available, bold wasn't available, and changing fonts meant changing the type ball or daisy wheel, which most operators wouldn't bother doing mid-document.

The underline was the only emphasis tool that worked. To create one, the typist would type the word, then backspace to the start of the word, and type a row of underscores (_) beneath it. The result was a manually-crafted underline that approximated what italics would have done in a printed book.

This led to the first widely-followed convention: in typewritten manuscripts, underline what would be italicized in print.

By the early 20th century, this convention had codified into style guides. The 1906 Chicago Manual of Style — and most others — instructed writers submitting manuscripts to publishers to underline:

• Book titles, magazine titles, newspapers
• Foreign words and phrases
• Words used as words ("the word and is overused")
• Internal monologue or thoughts
• Anything else that would be set in italics by the printer

Editors would receive the typewritten manuscript and replace the underlines with italics during typesetting. This survived for nearly a century.

Underlines as personal annotation

Outside of manuscripts, the underline thrived in everyday writing. Students underlined passages in textbooks. Lawyers underlined key clauses in contracts. Researchers underlined quotes in their notes. Letter-writers underlined emotionally charged words ("I really, really missed you").

The underline became the universal mark for "this matters" in handwritten notes — partly because it's the easiest emphasis to make: one quick stroke beneath a word.

By the mid-20th century, you could find underlines in:

• School essays (students emphasizing key arguments)
• Sermons (preachers marking up Bible passages)
• Recipes (cooks underlining critical instructions)
• Speeches (orators marking words to stress)
• Personal letters (writers heightening emotion)

Each context had its own informal conventions, but the underlying meaning was consistent: don't skip this.

The early computer era: underlines in monospace

When computers arrived in the 1960s and 70s, early text terminals were monospaced and supported very limited formatting. The underline survived for the same reason it did on typewriters — it was easier to render than italics on early character displays.

Many early word processors (WordStar, WordPerfect) treated underline as a primary formatting option, with a dedicated F-key shortcut. Documents from that era are full of underlined section headers, emphasized terms, and personal notes.

The convention from typewriter days carried over: in WordStar and similar early programs, underlining titles and foreign words was still standard.

The hyperlink era: a meaning shift

Then came 1989.

When Tim Berners-Lee designed the first web browsers and HTML, he needed a way to visually indicate that some text was a clickable link. He chose blue, underlined text.

Why blue? Practical reasons — early monitors had limited color palettes, and blue was distinguishable from black body text without being so bright it strained the eyes.

Why underlined? Because it was already universally recognized as "important / different from surrounding text." Users instinctively knew to look at it.

For the first decade of the web, this convention was nearly universal. Every clickable link was blue and underlined. Every underlined word in a webpage was clickable. The two associations became inseparable.

This created a problem that web typographers have wrestled with ever since: on the web, underlined text means "click me." Using underline for any other purpose — emphasis, titles, decorative effects — confuses readers who expect anything underlined to be interactive.

By the 2000s, most modern style guides for digital writing began discouraging underline for non-link emphasis. The Chicago Manual added a note. The AP Stylebook updated its recommendations. Web accessibility guidelines (WCAG) explicitly warned that underlining non-link text is misleading.

The era of CSS: precision underlining

CSS gave web designers fine-grained control over underlines:

• text-decoration: underline — the basic underline
• text-decoration-style: solid | dotted | dashed | wavy | double — different visual styles
• text-decoration-color: red — change the color independently of the text
• text-decoration-thickness: 2px — control the line weight
• text-underline-offset: 0.2em — adjust how far below the text the line sits
• text-decoration-skip-ink: auto — make the line skip through descenders (g, p, y) for cleaner look

These properties, fully supported in modern browsers since around 2018–2020, finally gave web designers the same level of underline control that typographers had in print. Modern websites use underline far more elegantly than the 1990s blue-underlined-link convention — including in places where underline is purely decorative.

The Unicode era: underlining anywhere

Meanwhile, in the world of plain text — text messages, social media, chat apps — underlining remained impossible for decades. Plain text doesn't carry formatting. There's no <u> tag in a tweet.

This changed with the widespread adoption of Unicode combining characters.

Unicode is the system that represents every character in every writing system on Earth (and a lot of symbols besides). Buried in its catalog are special combining marks — characters that don't appear on their own but attach themselves visually to the character before them. U+0332, the combining low line, draws a horizontal line beneath whatever character it's attached to.

When you type h̲e̲l̲l̲o̲, you're actually typing 10 characters: h, U+0332, e, U+0332, l, U+0332, l, U+0332, o, U+0332. Your device renders the result as underlined text.

This trick has existed since Unicode was first standardized in 1991, but it didn't see widespread use until smartphones — with their copy-paste functionality and Unicode-friendly text rendering — made it practical to use Unicode underlining in everyday messaging.

By the late 2010s, underline text generators (like the one you're reading this on) made it possible for anyone to underline text in any app: Instagram bios, WhatsApp statuses, Twitter posts, Discord usernames, etc. The underline returned to spaces it had never been able to live in before.

The underline today

In 2026, the underline carries a more layered set of meanings than at any point in its history:

• On the web: still primarily means hyperlink
• In print/style guides: discouraged in favor of italics for titles
• In documents (Word, Pages, Docs): a standard emphasis option, used widely
• In casual digital communication (chat, social): a decorative tool, often Unicode-based
• In academic and legal writing: still used for specific conventions (case citations, signatures, statutes)
• In hand-written notes: the fastest emphasis mark, alive and well

It's a remarkable arc for what's literally just a horizontal line. From scribal annotation to typewriter emphasis to hyperlink to Unicode decoration — the underline has adapted to every major shift in how we write, and it shows no sign of disappearing.

What to take away

The next time you underline a word, consider what you're invoking. Are you:

• Marking importance, like a medieval scribe?
• Substituting for italics, like a 1950s typewriter operator?
• Emphasizing on a screen, like a student annotating a PDF?
• Decorating an Instagram bio with Unicode flair?

All of these are valid uses. They're also all, in their own way, descendants of that single horizontal line that started showing up under important words a thousand years ago.

For decoration, emphasis, or just for fun — try our Underline Text Generator and add yourself to the long history of people underlining words to make them matter.

Frequently asked questions

Who invented the underline?

There's no single inventor. Underlining as an emphasis mark evolved gradually in medieval manuscript culture between roughly the 12th and 14th centuries, alongside other annotation conventions. Like most punctuation, it was a slowly-emerging consensus rather than someone's deliberate invention.

Is underlining considered old-fashioned today?

In some contexts, yes. Modern web typography style guides discourage underline for non-link emphasis, and most published books use italics rather than underlines for titles and emphasis. But underline remains common in casual writing, education, legal documents, and handwritten notes.

Why is blue the color of hyperlinks?

Tim Berners-Lee's original web browser used blue underlined text for links because blue was distinct from black body text on early CRT monitors and didn't strain the eyes as much as red or yellow. The convention spread quickly across browsers and became deeply ingrained.

Why do some style guides say to italicize, not underline, book titles?

Because italics is a more elegant typographic distinction than underlining, and modern word processors make italics easy to apply (which they weren't on typewriters). Most published style guides updated this rule between 1990 and 2010.

What's the difference between underline and underscore?

Underline is the visual mark — a line beneath text. Underscore (_) is a character used in computing to represent a space-like separator in identifiers (user_name, file_path). They look similar but have different uses.

Are there cultural differences in how underline is used?

Yes. In East Asian typography (Chinese, Japanese, Korean), underlining is less common than other emphasis methods like spacing the characters apart, using bold strokes, or adding emphasis marks (傍点 / 방점). Underline is mostly imported from Western typographic conventions in those scripts.

Try the underline tradition for yourself

Whether you're writing an Instagram bio, a Discord message, or a stylized text post, underlining has a way of making words land harder. Open our free Underline Text Generator, pick from 30+ styles, and join a thousand-year tradition of marking what matters.

For more on text formatting and typography, see our guides on underline vs italic vs bold and the accessibility of Unicode underlines.