The fourth in a series of global summit meetings focused on nuclear security — likely to be the last for some time — will occur in Washington March 31-April 1.  Meanwhile, recent events — including extended monitoring of a senior official of a facility with substantial stocks of HEU by Islamic State operatives — highlight the ever-evolving threat. Will the summit participants agree on approaches that will “keep this process alive and effective” after the summits end, as President Obama put it at the last summit?  Or will attention turn elsewhere, and nuclear security progress stall or even erode? In this MTA Seminar, Matthew Bunn will describe the ongoing threat, offer some previews of likely summit outcomes, and discuss some next steps to keep nuclear weapons and their essential ingredients out of terrorist hands.