Google Scholar provides a simple way to broadly search for scholarly literature. From one place, you can search across many disciplines and sources: articles, theses, books, abstracts and court opinions, from academic publishers, professional societies, online repositories, universities and other web sites. Google Scholar is not comprehensive but it does offer some useful features such as the ability to search for citing articles.
Don’t pay for it! Google Scholar often links to commercial publisher websites which ask you to pay for the full text.
How are documents ranked?
Should I rely on Google Scholar for all my research?
No - although Google Scholar can be useful, it is not comprehensive and we actually do not know what journals and books it covers (it is a Google secret!). It doesn’t search all scholarly content or journals, the "invisible or deep" web (most are in subscription databases), which is at least 500 times larger than the free web. This differs from library databases or Summon where we know the exact coverage of journals and books.
Searching is only by keyword, unlike library databases which have full controlled subject indexing and can offer special searching filters that are discipline-specific. You cannot limit to scholarly or peer-reviewed articles. Searching by date can be problematic.