 Apart from his teaching and publications, Kroll was an important agent for international collaboration in the classics.As an editor of important journals ("Bursian’s Jahresbericht über die Fortschritte der klassischen Altertumswissenschaft", 1898–1912; "Glotta", 1913–1936) and the "Realencyclopädie der Classischen Altertumswissenschaft" (1906–1939, as successor to Georg Wissowa) he collaborated with hundreds of scholars from all over Europe and the United States.He was one of the first German scholars to be invited to lecture in the United Kingdom after World War I, and was awarded a visiting professorship at the Princeton University in 1930/31.