Radicalism and extremism are frequently (mis-)used concepts. The meaning of these terms is vague and the boundaries between them and between either of these terms and mainstream political thoughts and practices are unclear. While there are no legal definitions of extremism or radicalism in most countries, there are nevertheless many governmental programs that deal with [Countering] Violent Extremism (CVE) and [De-]Radicalisation since both imply a turn to a specific form of political violence: terrorism. This Research Note presents the outcome of terminological and conceptual analyses of definitions of extremism and radicalism as utilised (mainly, but not exclusively) in Germany. The objective was to develop academic consensus definitions of these terms comparable to the approach developed by Alex P. Schmid for reaching an Academic Consensus Definition of Terrorism.