Restatements are highly authoritative commentary on legal issues that are primarily governed by case law. They are available in print and on Westlaw, Lexis, and HeinOnline (see the links below).
Each section of the Restatements contains a “black letter” statement of the law followed by explanatory comments and illustrations. Summaries of cases that interpret each section are included in the Appendix volumes (in print). Each appendix volume covers a specific time period. So, in order to find all the cases in a jurisdiction that interpret a section, you have to consult each appendix volume.
Lexis and HeinOnline, like the print Restatements, have separate files for the restatement rules and case summaries. However, Westlaw incorporates the case summaries into the file with the restatement rules.