Ms Chinchilla says she will continue the policies of the previous government
Costa Rica's first female president has been sworn into office in San Jose after winning elections in February.
Laura Chinchilla, 51, took her oath of office at an open-air ceremony in front of thousands of supporters.
The former vice-president has pledged to continue the free-market economic policies of her predecessor, Nobel laureate Oscar Arias.
She becomes the third female president in Central America after a landslide victory in elections.
Leading the centre-left National Liberation Party, she won 47% of the vote and had a 22-point lead over contender Otton Solis in February's election.
Joined by her husband, her parents and her 14-year old son on Saturday, Ms Chinchilla swore to uphold the country's constitution and accepted the presidential sash.
"I will work for a Costa Rica able to maintain moral leadership in the world thanks to defending peace, liberty and human rights," Costa Rican paper The Tico Times reported her as saying.
A number of world leaders attended the inauguration, including the presidents of Mexico, Colombia, Ecuador and Georgia.
A graduate of the University of Georgetown, Ms Chinchilla is a social conservative, opposing abortions and gay marriage.
She has pledged to tackle violent crime and drug-trafficking, and continue the economic policies of former President Arias which have enabled a trade pact with the US and commerce with China.
Mr Arias was awarded the Nobel peace prize in 1987 and has ruled the central American nation twice, most recently from 2006.