In the field of comparative law his methodological perspectives, particularly as articulated and disseminated by his students, including Ernst von Caemmerer [de], Gerhard Kegel [de], and Max Rheinstein, were influential in the development of the "functional" or "function/context" methodology that became standard in Europe, the United States, and elsewhere in the world, in the post-World War II era.
[7] His dissertation, written under Ludwig Mitteis [de], was entitled "Die Übertragbarkeit des Urheberrechts nach dem österreichischen Gesetzes vom 26.
[13][14] Most famously, his expertise in the field of comparative law led to his appointment, in 1926, as director of the newly created Kaiser Wilhelm Institute for Foreign and International Private Law (Kaiser-Wilhelm-Institut für ausländisches und internationales Privatrecht), in Berlin, one of the several independent research institutes founded by the Kaiser Wilhelm Society.
[22][23] In 1942 Rabel and German émigré colleague Karl Loewenstein were among those invited by the ALI to join an international experts' committee charged with preparing a global restatement of 'essential human rights.
'[24] The document that the ALI committee formulated[25] later was an important point of reference in the drafting of the Universal Declaration of Human Rights by the United Nations.
[26] After the war, while resident in the United States, Rabel completed what is considered to be his magnum opus, The Conflict of Laws: A Comparative Study, a four-volume work.
[21] He also spent time in Germany, both in Tübingen (where his old Institute had moved during the war), and in Berlin, where he taught at the Free University (Freie Universität).