Because film reviews appear in so many different types of publications, there is generally no single, authoritative strategy for locating them. Online coverage of newspapers and magazines, as well as scholarly periodicals, decreases as one goes back in time. Also, with the exception of the New York Times and the Times of London, newspapers only began publishing indexes in the late 1970s and early 1980s. In the course of your search you will probably have to consult a number of different resources in order to compile a comprehensive list of reviews.
The links provided here are broken down by release date (see tabs above) due to the varying film review coverage of particular resources and the varying reliability and extensiveness of electronic resources for film reviews. Below are the resources which overlap the time frames listed, and may be a good place to start your search.
The texts of older reviews will generally be unavailable online, with the notable exception of the New York Times:
Film Literature Index - 2 sources for content:
Reviews in print, early 1900's to present:
Find more reviews for this time period on the Where to Start tab above.
Find more reviews for this time period on the tab above.
For films released since the 1990's, search "Websites" page of this guide, as more recent films have the most reviews available online.