The short version
When you write **bold** and it renders as bold, that's Markdown. It was designed in 2004 as a way to write formatted text that's still readable as plain text. No menus, no toolbar, no clicking "B" for bold. You just type.
It's become the default writing format for most of the technical world. GitHub READMEs are Markdown. Notion, Obsidian, and Slack all support it. Documentation sites use it. If you've ever typed # Heading or - list item in a tool and it formatted automatically, you were writing Markdown.
How it works
Markdown uses punctuation characters to indicate formatting:
# Heading 1
## Heading 2
### Heading 3
**bold text**
*italic text*
- bullet point
- another bullet
1. numbered list
2. second item
[link text](https://example.com)
`inline code`
> blockquote
That's most of what you need. The full spec includes tables, images, footnotes, and task lists, but the basics above cover 90% of daily use.
Markdown files use the .md extension. They're plain text files, which means they work with any text editor, they're tiny, they're version-controllable with Git, and they'll be readable in 50 years. No proprietary format. No compatibility issues.
MDX is a variant that adds interactive components to Markdown. It's used in modern web frameworks to write content that can include live code examples, interactive charts, or custom UI elements.
Why it matters
If you work anywhere near tech, you'll write Markdown. GitHub requires it for README files and documentation. Most AI tools accept and output it. Knowledge management tools like Obsidian are built entirely on Markdown files. Learning the basic syntax takes 10 minutes and saves time every day.