The doctrines enunciated by the law have an important footing to protect the interests of justice, equity and good conscience and therefore such shall be valued and observed with great importance. Sometimes there exists two or more similar doctrines wherein a contingency is arisen as to validity of one over the other. Such a situation has likely to be crept up in instances where matters therein requires a strict interpretation of the provisions these are dealt with. Res judicata and estoppel both being equally paramount and indispensable, a difference of both stands scrutiny.
Before beginning with the points of differences it is essential to draw meaning of both these doctrines. Call it the doctrine of res judicata or the rule of conclusiveness of a judgement, it enacts rather mandates that once a matter is finally decided by a competent court, no party can be permitted to reopen it in a subsequent litigation. Acceding and acknowledging with the intent of the legislature and jurisprudential approach behind the mandatory provision, the Apex Court observed that, in the absence of rule of res judicata, there will be not end to litigation and the parties would be put to constant trouble, harassment and expenses. In simple words, the doctrine of res judicata operates as a bar on the jurisdiction of a court to try a suit which has been conclusively decided by the court with same parties, same subject matter and under same title. It is a bar on jurisdiction of a competent court. Meaning thereby that even if the court approached by litigants have appropriate jurisdiction than also such jurisdiction is barred because of the application of doctrine of res judicata. All these provisions are provided under section 11 of the Code of Civil Procedure,1908.
Whereas the doctrine estoppel as defined in Section 115 of the Indian Evidence Act, 1872 provides that “When one person has, by his declaration, act or omission, intentionally caused or permitted another person to believe a thing to be true and to act upon such belief, neither he nor his representative shall be allowed, in any suit or proceeding between himself and such person or his representative, to deny the truth of that thing.” The object of the legislature underlying the doctrine of estoppel is to prevent fraud and secure justice between the parties by promotion of honesty and good faith. Therefore when one person makes a misrepresentation to the other about a fact he would not be shut out by the rule of estoppel if that other person knew the true state of facts and must consequently not have been misled by the misrepresentation. But to understand and apply this concept there shall be some conditions precedent or existence of some salient features before applying the doctrine of estoppel. Firstly, one party should make a factual representation to the other party. Secondly, the other party should accept and rely upon the aforesaid factual representation. Thirdly, having relied on the aforesaid factual representation, the second party should alter his position. Fourthly, the instant altering of position should be such, that it would be iniquitous to require him to revert back to the original position. Therefore the doctrine of estoppel would apply only when, based on representation by the first party, the second party alters his position, in such manner, that it would be unfair to restore the initial position.
Having understood the meaning of both these doctrines, one similarity that can be observed that is both the doctrines are based for protecting of public interest. So the intent of the legislature can be said to be of the similar nature by putting into effect both these provisions in into their respective statues. In fact the doctrine of res judicata is often treated as a branch of law of estoppels. How res judicata can be considered to estop is by virtue of a previous judgement, after its coming into effect, an estoppel by verdict and an estoppel by a judgement. AS it has observed by the Supreme Court that the rule of constructive res judicata is nothing but a rule of estoppel, since constructive res judicata is a legal fiction created by the court wherein the matter in issue is treated as if it has been might and ought to have been the matter directly and substantially in issue in a subsequent suit.
The major point of differences, if considered can be drawn in terms for the point of origination, the reason for it development, authority, prohibitory value and binding nature. The point of origination of res judicata is a judgement in a former suit by the court whereas the estoppel is originated by the act of the parties themselves. The reason for the development of the doctrine of res judicata is for the public policy, which means an end to litigation, while the estoppel is rather based on the principles of equity, which means it bars the multiplicity of representations. On the other hand res judicata bars the multiplicity of suits.
Authoritatively, res judicata is a bar on the jurisdiction of a court, and is a basic test to institute a suit whereas, as mentioned before, estoppel is only a doctrine observed in evidence and disables the parties to speak further. In the lines of prohibitory values of both, both doctrines in one way or the other prohibits something, for which the res judicata prohibits a man averring the same thing in successive litigations whereas estoppel prevents a person from saying one thing which he has said before and consequences have arrived thereafter. And the last point of difference between both doctrines is the binding nature that can be showed by observing the doctrines in general. In res judicata, both the parties are subject to the application of res judicata since both has approached a subsequent court for the same matter to be adjudicated upon therefore its binding effect is on both the litigants. On the other hand, in case of estoppel, occurrence of a binding effect is only on the party who had made the previous statement or conduct through which the course of litigants have changed and thereby only that person will have to suffer the binding force.
 Supreme Court Employees’ Welfare Assn. v. Union of India AIR 1990 SC 334
 Maddanappa v. Chandramma AIR 1965 SC 1812
 Pratima Choudhary v. Kalpana Mukherjee AIR 2014 SC 1304
 Canada and Dominion Sugar Co. Ltd. V. Canadian National (West Indies) Steamships Ltd., 1947 AC 46 at p. 56 (PC)
 Batul Begum v. Hem Chander AIR 1960 All 519