We owe the first notion that ‘fascism’ was something generic and international to the interwar communist left. The ‘Report on Fascism’ was a series of important early documents on the - then emerging - phenomenon of Fascism in Italy.

Third International, “Report on Fascism”, IV Congress, 16 November 1922, http://www.international-communist-party.org/BasicTexts/English/22Fascis.htm; V Congress, 2 July 1924, http://www.international-communist-party.org/BasicTexts/English/24Fascis.htm.

In spite of their ideological obsessions, these documents provide the earliest attempt to understand fascism as a distinct political phenomenon. Fascism continued to inform discussion at the Communist International Congresses throughout most of the interwar period. Most of the documents from the Communist International congresses are available online: https://www.marxists.org/history/international/comintern//documents/volume2-1923-1928.pdf (1923-28); and https://www.marxists.org/history/international/comintern//documents/volume3-1929-1943.pdf (1929-43)

The now classic account by the Italian philosopher Umberto Eco of how something like ‘fascism’ may be a universal phenomenon and thus may resurface at any point, though in completely different  ideological and political guise.

Umberto Eco, Ur-Fascism, The New York Review, 22.6.1995, http://www.nybooks.com/articles/1995/06/22/ur-fascism/

 Ever since the recent financial crisis, there has been a tendency to compare the current rise of the radical and/or populist right with the rise and political success of fascism in the 1930s. See for example,

1. Martin Boon, Understanding the rise of the far right: Focus group results, Equality and Human Rights Commission, 2010, https://www.equalityhumanrights.com/sites/default/files/research-report-58-understanding-the-far-ight-focus-groups.pdf
2. Thilo Janssen, A love-hate relationship: far-right parties and the European Union, Rosa Luxemburg Stiftung, January 2016, http://www.rosalux-nyc.org/wp-content/files_mf/lovehaterelationship_thilo_janssen_english.pdf
3. The European Far Right: Historical and Contemporary Perspectives, ed by Giorgio's Charalambous, PRIO Report (2015) - http://file.prio.no/publication_files/cyprus/Far%20Right%20Report.pdf

There has also been a renewed interest in populism and the radical right following the EU referendum in Britain and the 2016 US Presidential elections. A number of excellent resources explore continuities and (reassuring) discontinuities between the crisis of liberalism in the 1930s and in the contemporary world. For example,

James McDougall, No, this isn't the 1930s - but yes, this is fascism", The Conversation, November 2016
http://theconversation.com/no-this-isnt-the-1930s-but-yes-this-is-fascism-68867
But interest in connections with the 1930s has also produced a series of excellent new resources on interwar fascism itself. A very useful special series of podcasts by Slate is dedicated to fascism as both a historical and a contemporary phenomenon, with different episodes dedicated to Italy, Spain, Germany, the U.K., Romania, and the contemporary world: Slate Academy, Fascism, http://www.slate.com/articles/slate_plus/fascism.html.