Google’s most recent Webmaster Central Blog post, entitled Better page titles in search results covers the basics of how page titles and descriptions (called snippets) are generated.
A few things to note:
In the New Year, Webmasters should take note that Google has updated their Site title and description page (including an eight minute video of Matt Cutts discussing optimizing websites for Google and snippets). This page also offers a solution for Webmasters frustrated with titles and descriptions they did not write appearing in search engine results pages (SERPs). If you have found that your titles or descriptions appearing in SERPs are sourced from the Open Directory Project (ODP), or DMOZ, there is a solution!
The following code, inserted in the head section of your code, will tell all robots not to display information from the ODP with regard to your snippets.
If you are only having an issue with Google displaying ODP data, use the following code:
Please note that this code will need to be crawled by the robots before you may see a change in the SERPs.
If you are unfamiliar with the ODP / DMOZ:
The Open Directory Project (http://www.dmoz.org) is a human-edited directory of the Web that is maintained by a global community of volunteer editors and is touted as the most comprehensive directory out there. There is no cost to submit your site to the ODP.