Although such operations are a very old and common practice, it is paradoxically not regulated by a single and coherent legal regime under international law.
Only the status of spies in times of war is, in fact, subject to specific international rules.
Because of this diversity, and of the absence of a single, general legal regime under international law, the problems raised by espionage require the examination of a different set of rules: sovereignty; nonintervention; use of force; sea, air, and space law; human rights; international economic law; international criminal law; etc.
Generally speaking, however, two types of approaches can be found in the doctrine.
While for a long time espionage essentially took place in the physical space, in the 21st century, it primarily takes place in the cyberspace.
It should also be noted that, against common assumptions, the notion exclusively refers to the gathering of information and does not refer to covert operations carried out by secret services more generally.
The first consists in a global approach, which examines espionage in a transversal way and in its various dimensions (see General Overviews).
The second, on the other hand, is a sectorial approach that tends to analyze specific espionage activities in light of a particular set of rules (see the other sections).
In face of these uncertainties, some authors have thus sought to establish abstract models for evaluation.
Deeks 2016 thus advocates for a “pragmatic” system that would determine the legality of acts of espionage depending on the interests at stake.