The first is religion and politics in the United States, with an emphasis on civil religion and presidential religious rhetoric. Among his published material you find monographs on Reagan and Bush Sr., as well as overviews of the role of religion in the White House (for example: Från Truman till Trump).
The second area is Swedish church history, with an emphasis on medieval and modern time.
Lejon has lectured in 12 countries, been a visiting professor in the U.S. for three years and published ca. 30 volumes along with a large number of articles.
He is the Head of History, Art History, Religious Studies.