There's also a handy group of meta tools that search multiple major engines at once so you don't have to hop site to site. Develop Favorite Engines Results from one search engine can vary dramatically with the results from another search engine. After trial and error, most people come to pick the few search engines that work with their research styles. Most importantly, the way you pose your question matters greatly to the particular search engine. Some practically require a Ph.D. in Boolean logic.
Some search engines return results with paid placements at the top of the list.
Most offer tips for conducting effective searches.