Res judicata and collateral estoppel may each have the effect of preventing consideration of an issue that has already been litigated and decided by a court. Although they are separate concepts, even courts sometimes have difficulty telling them apart. For that reason, it may be helpful to regard both as forms of issue preclusion. The following cases considered whether previous determination of an issue prevented further consideration of an identical or similar issue in a subsequent matter. In some, the court correctly or incorrectly used the term "res judicata," while in others it used the term "collateral estoppel." In many, the court used the phrase "issue preclusion" or words to that effect.