Examples of a few recent books on the subject. Use the Library Catalog to find hundreds more!
Journals, magazines, and newspapers.
Jus ad bellum -- The justification of and limits to the use of force.
Jus in bello -- Laws and legal norms governing battle and occupation.
Jus post bellum -- Justice during war termination
--What are Jus ad Bellum and Jus in Bello? (ICRC)
--Short explanations from the Crimes of War project.
--Geneva Conventions and Updated Commentaries (ICRC)