Antifa is the label that's currently in vogue for militant communist and anarchist street protestors. Like many labels used by the media, it doesn't stick equally well to every person or group to which it is applied. Groups calling themselves antifa may or may not be affiliated with the successors of the original German Anti-Fascist Action group, which was the street-fighting arm of the German Communist Party set up in the early 1930's specifically to fight Nazis. I don't know anything about the lineage of the various successor groups, but there have certainly been Antifa groups active in continental Europe for a long time. People who are labeled "Antifa" in 2017 are probably the same type of people who formed the Blac Bloc of the 2010 Toronto G20 protests: students who have read maybe a little too much Marx or Marxist criticism. "Antifa" is preferred over "Blac Bloc" in 2017 It's only because many people have been convinced that Donald Trump is a Hitler and his supporters Nazis (many actual far-right were convinced too, though this excited them instead of terrifying them) that the militant left has decided to brand itself as anti-fascist in opposition to Trump's association with fascism.