They began with a visit to the official residence of Ireland's longtime president before meeting with the country's prime minister.
"The friendship and the bond between the United States and Ireland could not be stronger. Obviously, it is not just a matter of strategic interest. It's not just a matter of foreign policy," the president said in a news conference. "For the United States, Ireland carries a blood link with it."
The trip is not all business. The Obamas also traveled to the tiny town of Moneygall, which is the birthplace of his great-great-great grandfather on his mother's side, Falmouth Kearney. Kearney lived there until immigrating to the U.S. in 1850 at the height of Ireland's Great Famine.
The president raised a pint of Guinness in Ollie's Bar, held up a baby and shook innumerable hands. He took a look at Kearney's baptism records - the documents that established his connection to the town - and even got to meet, hug and drink with a distant family member: Henry Healy, a 26-year-old accountant for a plumbing firm.
Guinness last week delivered a specially brewed keg of stout to be poured the moment Obama walked through the door of Ollie's Bar, which sports a bronze bust and life-size photo cutout of the president.
After Dublin, Obama heads to London for a two-day state visit at the invitation of the queen. He'll then travel to Deauville, France, to meet with the heads of leading industrial nations, before ending his Europe trip with a visit to Poland, a strategically important Central European ally.
The Associated Press contributed to this story.