The primary aim of observance of international law lies with the state as they do observe international laws in our municipal laws, but if they are not been observed, the court apply these principles through the theory of implied adoption but those principles should not be inconsistent with the constitution and the law enacted by the legislature. If there occurs a conflict between international law and municipal law, the court shall always follow the municipal law. as referred in the case of Gramophone co. of India Ltd v/s birendra bahadur pandey  as Indian judiciary is not empowered to make legislations but it interprets India’s obligation in international law by pronouncing decisions in municipal or local cases by concerning issues of international law. So Indian judiciary has been playing a very active role in implementing India’s international obligations under international treaties.
It has been categorized into two parts as:
Prevailing Customary International Laws
Our Indian constitution contains a specific provision in article 51 which is a direction to state, which actually shows the intention of our law makers(founding fathers) towards international law which reads as under: “ Promotion Of International Peace And Security-The state shall endeavor to-
(a) Promote international peace and security;
(b) Maintain just and honourable relations between nations;
(c) Foster respect for international law and treaty obligations in the dealings of organised peoples with one another; and
(d) Encourage settlement of international disputes by arbitration.
In case of keshavanand bharti v/s state of kerala  Chief Justice Sikri observed that: “It seems to me that, in view of article 51 of the directive principles, this court must interpret language of the constitution, if not intractable, which is after all a municipal law, in the light of the United Nations Charter and the solemn declaration subscribed to by India”. from the above judgment it can be deduced that where the language of the municipal law is ambiguous or rather intractable the court must rely upon the parent international authority of municipal law. as article 253 of our Indian constitution confers exclusive power upon parliament to make law for giving effect to any treaty, agreement or convention with any other country or countries or any decisions made at any international conference.
Article 51 directs the state to respect international law although it does not make international law as a part of Indian law. Article 51 is a directive principle i.e. it is to be read with article 37 of constitution of India which lays down the provisions contained in part iv shall not be enforceable in any courts but the principles therein laid down are nevertheless fundamental in governance of the country and it shall be the duty of the state to apply these principles in making laws.
Thus if there occurs a conflict between the international and the municipal law, the courts shall as far as possible shall try to provide a harmonious construction between the two laws. this view has been taken by the Calcutta high court in krishna sharma v/s state of west benga  Whereas in the case of ADM Jabalpur v/s Shivkant Shukla ( Habeous corpus case)  the Honble Supreme Court has taken the view that “nothing which conflicts with the provision of our constitution could be enforced her under any disguise”
Taking the liberal approach the Honble Supreme Court in the case of Gramophone Co of India V/S Birendra Bahadur Pandey  has laid down that the comity of nations requires that the rules of international law may be accommodated in the municipal law even without express legislative sanctions provided they do not run conflict with the acts of parliament …the doctrine of incorporation also recognizes the position that the rules of international law are incorporated into the nations law and considered to be part of national law , unless they are in conflicts with an act of parliament.
The height of judicial creativity is enshrined In the case of Vellore citizens welfare forum V. Union of India  , the Honble Supreme Court upholding the validity of principles of sustainable development , polluter pays and precautionary rules has laid down “ once these principles are accepted as part of customary international law, there should be no difficulties in accepting them as part of our domestic law. It is almost an accepted preposition of law that the rules of customary international law, which are not contrary to the municipal law shall be deemed to have been incorporated in the domestic law and shall be followed by the court of law.” The same view has been taken by the Honble Supreme Court in the case of People Union for Civil Liberties V. Union Of India  .
Thus it can deduced from the above judgment that the courts while applying the rules of international customary law have craft them in the Indian domestic law.
Implementation of treaty obligation
The basic question which arose for the implementation of international law covenants, treaties is that whether the treaties are automatically binding on india or they need any enabling legislation.
Answer to this question lies in the judgement given by the hon’ble court in the case of Jolly George Verghese and othrs vs Bank of Coachin  . The hon’ble supreme court, through the words of Justice Krishna Iyer had laid down that “the positive commitment of state parties is in the legislative action at home but does not automatically covenant and enforceable part of corpus juris in India”.
On the practical note it has been observed that international treaties have been used in aid of domestic laws. Such treaties are been used for the following purposes.
To fill a gap in the law
As the mean of interpretation
To justify and fortify a stance taken
To implement international convention when they are not in conflict with existing national laws.
To fulfill the spirit of the conventions and treaties
To interpret the law as to reflect international changes
The judicial activism in the field of implementation of international treaties can be marked from the leading case of Vishakha vs. State of Rajasthan  . The hon’ble apex court while promulgating the guidelines on women’s sexual harassment has observed “in the absence of domestic law, occupying the field to formulate effective measures to check the evil of sexual harassment of working women at all work places, the contents of internation conventions and norms are significant for the purpose of interpretation of the guarantee of gender equality, right to work with human dignity in Article 14, 15 , 19(1)(g) and 21 of the constitution and the safeguard against the sexual harassment implicit there in. any international convention not in consistence with the fundamental rights and in harmony there of to promote the object of constitutional guarantee”.
It can be observed from above case that the court can apply international treaties to the provisions of domestic law, if they are not in conflict with municipal law. In another case of Neelabati Behera vs. State of Orissa  the hon’ble supreme court while granting compensation for custodial death has laid down its backing on Article 9(5) on the conventions on civil and political rights. In another case of Chairman Railway Board vs. Chandrima Das,  , the hon’ble supreme court while expanding the scope of article 21 of the constitution by providing protection to foreign rape victim and referred to the international convention and declaration of human rights. In another case the court has asserted that the application of UDHR, and principles thereof may have to be read, if need be, into the domestic jurisprudence.
It would be better to conclude and precisely to say that the international treaties are enforceable by the Indian courts when they are incorporated by international law by the act of parliament. There are number of legislations which are constituted after india became the signatory to such international covenants and treaties, eg: Diplomatic Relation (Vienna Conventions) Act 1972. SAARC Convention (separation of terrorism) Act 1993, Protection Of Human Rights Act 1993. Some other acts on territorial waters, exclusive economic zone etc.
It would not be wrong to say in recent years indian judiciary had relied upon international treaties and conventions un less they are not in conflict with the Indian national laws.