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Host nation Germany has billed the two-day meeting as a chance for the club of leading economies to discuss how to work together on challenges ranging from climate change to the conflicts in Syria, Ukraine and Yemen.
But all eyes will be on America's top diplomat, whose maiden trip to Europe will bring him face-to-face with allies seeking reassurance that President Donald Trump will not upend decades of US foreign policy despite his fiery campaign rhetoric.
Tillerson will also have his first sit-down with Russian Foreign Minister Sergei Lavrov in Bonn, talks that will be closely scrutinised for any hint of a rapprochement as controversy swirls over White House ties to the Kremlin.
The Texan could also face questions about the Israeli-Palestinian conflict, after Trump caused international consternation yesterday by dropping Washington's years-long quest for a two-state solution, saying he would back a single state if it led to peace.
US relations with China are likewise in the spotlight.The G20 gathering could see Tillerson's first encounter with Chinese Foreign Minister Wang Yi, whose attendance was only confirmed days earlier following a conciliatory phone call between Trump and President Xi Jinping.
During the call, Trump reaffirmed US adherence to the decades-old position that Taiwan is not separate from China, backtracking on earlier comments that cast doubt on the "One China" principle.
US Defence Secretary James Mattis is attending the second day of a NATO meeting in Brussels Thursday, while Vice President Mike Pence will be the highest-ranking US official participating in the Munich Security Conference from Friday.
"There are plenty of uncertainties about what they want, what they plan," a European diplomat said about the Trump administration. "We hope we'll get some clarity in the weeks to come.