Org supports links to files, websites, Usenet and email messages, BBDB database entries and links to both IRC conversations and their logs. External links are URL-like locators. They start with a short identifying string followed by a colon. There can be no space after the colon. The following list shows examples for each link type.
http://www.astro.uva.nl/~dominik on the web
doi:10.1000/182 DOI for an electronic resource
file:/home/dominik/images/jupiter.jpg file, absolute path
/home/dominik/images/jupiter.jpg same as above
file:papers/last.pdf file, relative path
./papers/last.pdf same as above
file:/myself@some.where:papers/last.pdf file, path on remote machine
/myself@some.where:papers/last.pdf same as above
file:sometextfile::NNN file with line number to jump to
file:projects.org another Org file
file:projects.org::some words text search in Org file
file:projects.org::*task title heading search in Org file
docview:papers/last.pdf::NNN open file in doc-view mode at page NNN
id:B7423F4D-2E8A-471B-8810-C40F074717E9 Link to heading by ID
news:comp.emacs Usenet link
mailto:adent@galaxy.net Mail link
vm:folder VM folder link
vm:folder#id VM message link
vm://myself@some.where.org/folder#id VM on remote machine
wl:folder WANDERLUST folder link
wl:folder#id WANDERLUST message link
mhe:folder MH-E folder link
mhe:folder#id MH-E message link
rmail:folder RMAIL folder link
rmail:folder#id RMAIL message link
gnus:group Gnus group link
gnus:group#id Gnus article link
bbdb:R.*Stallman BBDB link (with regexp)
irc:/irc.com/#emacs/bob IRC link
info:org:External%20links Info node link (with encoded space)
shell:ls *.org A shell command
elisp:org-agenda Interactive Elisp command
elisp:(find-file-other-frame "Elisp.org") Elisp form to evaluate
A link should be enclosed in double brackets and may contain a descriptive text to be displayed instead of the URL (see Link format), for example:
[[http://www.gnu.org/software/emacs/][GNU Emacs]]
If the description is a file name or URL that points to an image, HTML export (see HTML export) will inline the image as a clickable button. If there is no description at all and the link points to an image, that image will be inlined into the exported HTML file.
Org also finds external links in the normal text and activates them as links. If spaces must be part of the link (for example in ‘bbdb:Richard Stallman’), or if you need to remove ambiguities about the end of the link, enclose them in square brackets.