What type of law?

Some of the Hague Conventions deal with the determination of the applicable law, some with the conflict of jurisdictions, some with the recognition and enforcement of foreign judgments and some with administrative and judicial co-operation between authorities, and some combine one or more of these aspects of private international law.
Not all Conventions concluded at The Hague are Conventions of the Hague Conference on Private International Law (e.g. the Hague Conventions of 1964 relating to a Uniform Law on the International Sale of Goods (ULIS) and relating to a Uniform Law on the Formation of Contracts for the International Sale of Goods (ULF)).