Glossary
Discovery
The pre-trial process where each side gets to find out what evidence the other side has. Tools include written questions (interrogatories), document requests, depositions, and subpoenas to non-parties.
Discovery is the longest phase of most civil cases. The idea is to prevent "trial by surprise": both sides should know what the witnesses will say and what the documents look like before the trial starts.
Discovery can take months or years. It often costs more than the trial itself. Disputes about what has to be produced and what's privileged from disclosure are some of the most contested parts of any litigation.
Pro se parties have the same right to use discovery as represented parties: but the procedures are technical, and missing a deadline or filing the wrong thing can hurt your case.