Modern-day IHL is generally considered to have developed from two main sources: the law of Geneva, a body of humanitarian rules protecting victims of armed conflict, and the law of The Hague, legal principles concerning the conduct of hostilities.

Geneva Law is a body of humanitarian rules protecting victims of war and is outlined above. It establishes the rights and obligations relating to the protection of particular groups affected by, or involved in, armed conflict, eg. combatants, civilians, medics, POWs and injured combatants.
 
Hague Law concerns the conduct of hostilities. It establishes the rights and obligations of armed forces in their military operations and limits the means of harming the enemy.

Today, modern IHL is considered to contain elements from both branches of law as the Additional Protocols to the Geneva Conventions incorporate important parts of Hague Law.



Useful links:

More information on the Law of Geneva and Law of The Hague
Complete text of the 1899-1954 Hague Conventions