Good article on Res Judicata, stay of suit and estoppel
S 11 of CPC embodies the important doctrine of res judicata. It provides that no court shall try any suit or issue ,in which the matter directly and substantially in issue has been directly and substantially in issue in a former suit between the same parties(or between parties under whom they or any of them,litigating under the same title) in a competent court, and has been heard and finally decided by such a court.
1)The former suit means suit which has been decided prior to the suit in question, whether or not it was instituted prior thereto.
2)Any relief claimed in the plaint which is not expressly granted by the decree is deemed to have been refused.
3)Provisions of this section are also applicable to execution proceeding.
4) An issue which has been heard and finally decided by a court of limited jurisdiction, competent to decide such issue, operates as res judicata in a subsequent suit, notwithstanding that such court of limited jurisdiction was not competent to try such subsequent suit or the suit in which such issue has been subsequently raised.