According to Reuters, Obama described Merkel as his "closest international partner" shortly before jetting off to Germany.
Obama has also used the trip as an opportunity to remind President-elect Donald Trump that he might want to cool it on some of the more controversial claims he made on his campaign trail now that he is actually headed to the White House.
"What makes me cautiously optimistic about my successor and the shift from campaign mode to governance is there is something about the solemn responsibilities of that office ... that it forces you to focus," Obama said.
In particular, Obama encouraged Trump to hold firm on the US' relationship with Moscow.
Trump himself met with Obama last week, when the two men were understood to have put aside their differences in a bid to smooth out any bumps in the transition period.