In his weekly radio and Internet address, the president said in the days since two bombs exploded at the marathon finish line, killing three people and injuring more than 170, "the world has witnessed one sure and steadfast truth: Americans refuse to be terrorized."
"Ultimately, that's what we'll remember from this week," he said. "That's what will remain. Stories of heroism and kindness; resolve and resilience; generosity and love."
Obama commended "the brave first responders -- police officers, firefighters, EMTs, and National Guard -- who ran toward danger to help their fellow citizens," as well as "race volunteers, spectators and exhausted runners who rushed to help, including troops and veterans who never expected to see such scenes on the streets of America."
The president also commended "the determined doctors and nurses at some of the world's best hospitals, who have toiled day and night to save so many lives" and "the big-hearted people of Boston -- residents, priests, shopkeepers -- who carried victims in their arms; delivered water and blankets; lined up to give blood; opened their homes to total strangers."
He also praised "the heroic federal agents and police officers who worked together throughout the week, often at great risk to themselves, to keep our communities safe."
"As a country, we are eternally grateful for the profound sacrifices they make in the line of duty -- sometimes making the ultimate sacrifice to defend the people they've sworn to protect," Obama said.
"If anyone wants to know who we are; what America is; how we respond to evil and terror -- that's it," the president said. "Selflessly. Compassionately. And unafraid."
He said Boston's strength "remains undaunted" and America's spirit "remains undimmed."
"In the days to come, we will remain vigilant as a nation," Obama said. "And I have no doubt the city of Boston and its surrounding communities will continue to respond in the same proud and heroic way that they have thus far -- and their fellow Americans will be right there with them every step of the way."