The United Nations Treaty Collection contains the texts of all major multilateral treaties entered into by UN Member States and deposited with the Secretary General of the United Nations, as well as the relevant ratifications and declarations. The database is searchable by treaty title, popular name, keyword, Member State, and action (such as signature, entry into force or withdrawal of declaration).
The UN High Commission for Human Rights provides a list of the all major international human rights treaties, with links. For general (not case-specific) interpretation of the core international human rights treaties, see the UN treaty bodies’ General Comments.
The International Committee of the Red Cross maintains a searchable database of treaties on international humanitarian law.
In addition, the instruments relevant to each regional human rights system can be found on the websites of the following bodies: