About 500 experts from more than 70 nations are holding talks in Paris on how to choke off financing for the Islamic State group and Al-Qaida.
Wednesday's meeting opens a two-day international conference championed by French President Emmanuel Macron under the banner "No Money for Terror."
Islamic State revenues alone are estimated at $2.5 billion between 2014 and 2016, according to the French president's office.
The French organizers are pushing for international coordination and more transparency in financial transactions, as terror groups use increasingly sophisticated methods to transfer money.
On Thursday, the conference will gather ministers of justice, finance, foreign affairs and the interior from Western countries, the Arab world and other nationsm as well as representatives of 18 international organizations.
The meetings come as international donors in Brussels are drumming up aid for conflict-ravaged Syria.