Here are some of the condolences and reactions to her passing.
"I'm missing my mother-in-law and role model tonight," tweeted former first lady Laura Bush.
"The world is poorer without her in it."
Former President George W. Bush's Instagram account contained a photo of his parents.
"Laura, Barbara, Jenna, and I are sad, but our souls are settled because we know hers was," he said in a statement.
George P. Bush, Bush's grandson tweeted: "My grandmother's entire life was focused on others. For my grandfather, she was his top adviser and confidante. For her family, she was a steady, loving and guiding hand."
Jenna Hager, her granddaughter wrote: "I already miss this FORCE of a woman— the 'enforcer' because she was the glue that held our family together. She taught me to use my voice but also to value the opinions of others."
NFL player JJ Watt tweeted about Bush: "You were a beautiful light in this world and I am forever thankful for your friendship."
Houston mayor Sylvester Turner tweeted: "In her loving memory, the City of Houston and the Houston Public Library Foundation will work to complete the master planned improvements to the Barbara Bush Literacy Plaza in front of the Jesse H. Jones Central Library."
Bush advocated for literacy and raised awareness of the issue. She launched a nonprofit for family literacy that encouraged reading and writing in low-income households and wrote books, including a children's book about their family dog, Millie.
The Texas Rangers, the baseball team, tweeted a photo of Bush throwing out the ceremonial first pitch wearing its team jacket. "She will forever be in our hearts," the team tweeted.
The King Center posted a photo of Barbara Bush seated next to the late Coretta Scott King.
"May the family be comforted by sweet memories and encouraged by the love that former First Lady #BarbaraBush deposited," it tweeted.
Maria Shriver wrote that Bush had "served her country with class. She served her family with love and compassion. I'm grateful I knew her."
The US State Department tweeted a quote from ones of its spokespersons: "Barbara Bush represented the best of our country to the world, from our embassy in China to @WhiteHouse as First Lady. We're grateful for her legacy of public service, volunteerism & family."
Rev. Jesse Jackson Sr. tweeted: "May she rest in heavenly peace."