Illan works on questions of protest, public order and critical legal theory. His latest book is Law & Disorder: Sovereignty, Protest, Atmosphere is published by Routledge. The book focuses on the moment when social unrest takes hold of a populace, bringing the state structures of government and sovereignty into question. It develops the idea that moods, atmospheres, affects and public feelings are crucial to understand the way in which sovereignty and protest work for the populace.

He has published on critical legal theory, affective dynamics of policing, theories of constituent power, the Arab Spring, protest and transitional justice in Colombia, theories of human rights and revolt, and new Andean constitutional apparatuses.