Documentation for JIRA 4.1. Documentation for other versions of JIRA is available too.
To import issue data from CSV (Comma-Separated Value), Bugzilla, FogBugz or Mantis, please see the documentation:
For other types of import, please contact us as we may have done it before. See also JIRA's Jelly support — Jelly is a scriptable interface to JIRA that is useful for importing data.