The validity of a contract is legally binding on the parties, and making the contract legally binding is the most basic and important requirement for the parties to conclude a contract. Article 2 of the Contract Law of People's Republic of China (PRC) (hereinafter referred to as the Contract Law) stipulates that the contract referred to in this Law is an agreement between natural persons, legal persons and other organizations with equal subjects to establish, change and terminate civil rights and obligations. Article 85 of General Principles of Civil Law of People's Republic of China (PRC) (hereinafter referred to as General Principles of Civil Law) stipulates that a contract is an agreement between the parties to establish, change and terminate civil rights and obligations. According to the definition of contract in the General Principles of Civil Law, some scholars believe that the word "agreement" should contain double meanings: one is contract, and the other is agreement. Therefore, some scholars believe that the contract is essentially an agreement, and the establishment of the contract is the agreement of the parties on the meaning, which should be said to be more correct. Then, how to make the contract (that is, the agreement between the parties) recognized and protected by law is an important topic that both legal theory and judicial practice should pay attention to. Because of the conflict between judicial interpretation and legal provisions, as well as the inconsistent or even chaotic understanding of the theory of contract validity in judicial practice, it is of great practical guiding significance to study it.

One of the main purposes of contract law is to protect the legitimate rights and interests of the parties, maintain social and economic order and promote socialist modernization. Article 85 of the General Principles of the Civil Law stipulates that legally established contracts are protected by law. Article 8 of the Contract Law stipulates that a legally established contract is legally binding on the parties. They all specify the legal protection of legally established contracts. Therefore, the determination of the validity of the contract has become one of the specific contents of the state's recognition, protection and intervention in the contract. The so-called contract validity refers to the binding force of the rights and obligations stipulated in the contract, which exists in the whole process of the contract from effective to invalid. According to the theory of contract law, the current provisions of contract law and judicial practice, we can divide the validity of contracts into four types: valid contracts, invalid contracts, contracts with pending validity and revocable contracts, and correspondingly produce four kinds of valid contracts. In this paper, the corresponding specific research is carried out according to different effective conditions.

I. Overview of the effectiveness of the contract: the concept, effectiveness and types of the contract;

Second, the relationship and characteristics between the establishment and effectiveness of the contract;

Three. Validity of contract: concept, characteristics and conditions;

4. Invalid contract: the concept, characteristics, causes and classification of invalid contract;

Verb (abbreviation for verb) Contract with undetermined validity: concept, characteristics, requirements and performance types;

6. Revocable contract: concept, characteristics and exercise of rights;

7. The relationship between revocable contract and invalid contract;

Eight, the legal consequences after the contract is confirmed to be invalid and revoked;

Nine. Special discussion and evaluation of contract validity confirmation under several specific circumstances