It is often useful to link issues together (both bidirectionally and unidirectionally).

Basically you would define different 'link types' like "A blocks B <> B blocked by A" and "A depends on B <> B depended on by A" etc (customise any types you want). We'll provide some defaults like 'blocker' and 'dependency'.

(Should links always be bi-directional? I think so)

Then the view issue interface would display all the linked issues, with their link type (allowing you to thus easily navigate around the 'issue graph'!).

To add links, we'd provide a simple link issue interface. Basically a single select box to select link type, and either enter the issue key into a text field, or select one of your 'history' links! (See JRA-520)

It's a little like Bugzilla's 'blocker' feature, but much more powerful.