The is a summary of the official Markdown syntax document.
You can put real HTML anywhere in a Markdown document, but block-level elements (div, table, pre, p) need a blank line before and after. Also, markdown syntax inside HTML is not processed.
& and <, (and many other special characters) are automatically translated to HTML entities (&).
Paragraphs are separated by blank lines.
Non-paragraph line breaks (<br />) can be made by putting 2 spaces after the line.
Header H1 ========= Header H2 --------- # Header H1 # ## Header H2 ## ### Header H3 ### #### Header H4 #### > A blockquote > > A nested blockquote * Bulleted list * Bulleted list * Bulleted list 1. Numbered list 1 2. Numbered list Sub-paragraphs within list items must be indented 4 spaces. 2. Numbered list (actual numbers don't matter) Use *single asterisks* or _underscores_ for <em>. Use **double asterisks** or __doubled underscores__ for <strong>. A horizontal rule: --------------- `backticks` are for <code>. Indent pre-formatted blocks 4 spaces. The carrot-ed URL <http://paulgorman.org> will be hyperlinked. [This](http://paulgorman.org) will be hyperlinked. A link within the same document works like [this][foo], and links to the paragraph below. [foo]: This is the target of a link withing the same document.  
Use a backslash to escape any literal character that's wrongly interpreted as markdown.
Besides `markdown.pl`, a number of processors are available, like Pandoc and kramdown. The other processors support extensions for the markdown syntax.
Definition lists are like this: A term : The definition Another term : Another definition
Pandoc outputs HTML like pandoc -S5 input.txt -o output.html (-S outputs dash and ellipses as entities, and -5 generates HTML5 instead of 4), or LaTeX like pandoc input.txt -o output.tex. The -s option adds standard headers and footers to the output, rather than a fragment. The -t and -f explicitly specify the to and from formats, like pandoc -f html -t makrdown input.html to output HTML as markdown.
If no output file is specified, results go to stdout.
The --smart option converts straight quotes to curly quotes,
--- and -- to Em-dashes, and ... to ellipses.
<!-- HTML comments work -->
Right Left Center Default
------- ------ ---------- -------
12 12 12 12
123 123 123 123
1 1 1 1
Table: Demonstration of simple table syntax.
Multi-line tables are also supported:
-------------------------------------------------------------
Centered Default Right Left
Header Aligned Aligned Aligned
----------- ------- --------------- -------------------------
First row 12.0 Example of a row that
spans multiple lines.
Second row 5.0 Here's another one. Note
the blank line between
rows.
-------------------------------------------------------------
Table: Here's the caption. It, too, may span
multiple lines.
Document header:
% title
% author(s) (separated by semicolons)
% date
--- renders as an em-dash
-- renders as an en-dash
... renders as an ellipsis
{::comment}
A comment ignored by kramdown
{:/comment}
| Table header 1 | Table header 2 | Table header 3 | Table header 4 |
|:---------------|:--------------:|---------------:|----------------|
| left aligned | center aligned | right aligned | default align |