Intertemporal Law is a concept in the field of legal theory.
It deals with the complications caused by alleged abuse or violation of collective or individual rights in the historical past, in a territory where the legal system has undergone significant changes since then, and a redress along the lines of the current legal regime is virtually impossible.
The origins of Intertemporal Law as a legal theoretical concept, especially in relation to the use of force, are to be found in CJ Huber's discussion in the Palmas Arbitration case. (Islands of Palmas Arbitration, Netherlands v US, 1928) where he stated "a juridical fact must be appreciated in the light of the law contemporary with it."
Another definition
Intertemporal law can be more broadly defined as the branch of law which governs the usage of treaties, codifications and legal acts to the cases which occurred before their creation or entry into force. It existed in Roman law, which caused the phrase "lex retro non agit" (law does not work backward) to be coined. The principle is currently applied in several branches of law, sometimes with modifications, such as the Polish criminal code, where the principle "lex severior retro non agit" - stricter law does not work backward - is used.