WordPress, founded in 2003 by Matt Mullenberg, was initially a blogging system, but has grown to a flexible website platform. Joomla, released since 2005, has a mission to provide a flexible platform for digital publishing and collaboration. Comparing subjects such as marketshare, themes, plugins, security or (un)recommended usage, you’ll get a good picture of each system and how and when to use them.
Source: WordPress vs Joomla! CMS comparison by Web Whales.
