Google has launched a new service that allows users to create customized search engines.

The Google Custom Search Engine lets users specify the parameters of where and what Google searches, allowing users to create search engines devoted to one specific topic or group of sites, such as a list of favorite blogs or retail sites.

"We want to make it easy for anyone to create a search engine about all their favorite topics, without needing a PhD," said Google's vice president of search products and user experience, Marissa Mayer.

To set up the Custom Search Engine, the user specifies the title, summary, keywords and a list of domains to search. Users have the option of either limiting the results to the listed domains, or having them presented on the top of other Google results.

If users want to tweak the way the searches run further, they can add annotations to certain sites, which helps to separate results or give results from certain sites a higher position.

Users also have the option of editing the Custom Search Engine information as an XML file and uploading it directly, as well as embedding the Custom Search Engine in their own web pages.

The company said that only non-profits, universities and government agencies will be able to block ads from appearing on the results page. For other users, Google is offering the option of connecting an Adsense account into the engine, allowing the user to make money from clicks originating from their search engine pages.