Claim & Issue Preclusion
The two can almost be thought of as a civil version of double jeopardy.
Claim preclusion is the doctrine that prevents a plaintiff from re-litigating a claim.
It is most commonly asserted by the defendant.
In order for the doctrine to apply, the parties must be largely the same and the claim must have been previously decided.
To determine if the parties are the same, one looks to the original defendant and plaintiff.
If the plaintiffs don't match up from lawsuit to lawsuit, the motion to dismiss based on res judicata will most likely fail since the current plaintiff has not actually litigated his or her claim before.
If the defendants match up and the plaintiffs match up, it is somewhat easy to see that the claim should be precluded based on the same parties.
The other part of claim preclusion rests on whether the claim had previously been brought and decided.
In this area, there are more difficulties since there are sometimes conflicting definitions of what a "claim" is.
California, for example, uses a definition that counts each injury to a different item as a different potential claim.
So a person can bring one lawsuit for an injury to his or her person and a different, later lawsuit for an injury to a car.
The definition adopted by California is largely out of favor because of the liberal joinder rules.
More commonly, courts have adopted a definition that says that if the injuries are all from the same event and the same parties, they are the same claim.
This does not mean that the plaintiff may not sue later for a different incident but after the first lawsuit, the claims not brought during that lawsuit for that event are dead.
Issue preclusion, on the other hand, is largely used by the plaintiff in a lawsuit.
This doctrine, also known as collateral estoppel, prevents the parties from re-litigating a point that has already been decided in a previous case.
For example, an individual that goes to a criminal trial for committing some crime cannot relitigate whether or not he or she actually committed some action in the later civil trial as this was already determined to be true by a jury.
An exception to this rule is when the defendant participates in a civil trial first and a criminal trial second.
Because the civil courts use a lower burden of proof than the criminal ones do, the transfer does not work and so the defendant can defend on that count.