His work has been characterized as an "interrogation of political liberalism in the United States and Europe—asking for definition of its many forms, their origins, their strengths and weaknesses, and what kinds there can be".

Among his influences, he includes Richard Hofstadter, Ralf Dahrendorf, Robert Dahl, and Daniel Bell.

[15] Katznelson has written or co-written ten books, co-edited several others, and published over sixty journal articles.

He questions "when and why liberal democracies become normatively appealing (less closed and more tolerant) and more effective (less vulnerable and more secure).

[17] His book Liberalism’s Crooked Circle: Letters to Adam Michnik (1996) won American Political Science Association's (APSA) Michael Harrington Prize.