Zdeněk Kárník initially focused on the history of the workers' movement and socialist parties, extending his interest later on to the history of the First and Second Czechoslovak Republics (1918-1939) in relation to the period of the existence of Austria-Hungary: Socialisté na rozcestí: Habsburk, Masaryk či Šmeral?
Zdeněk Kárník has also contributed to the periodicals Památkářské práce (Heritage Works), Acta Oeconomica Pragensia, Historický obzor (Historical Horizon), Východočeské listy historické (Eastern Bohemian Historical Letters), Acta historica et museologica Universitatis Silesianae Opaviensis et al., to the Larousse encyclopaedia, and a number of collections and publications focusing on heritage preservation.