After the death of Ansel's grandfather and the aftermath of the Panic of 1907, his father's business suffered great financial losses. By 1912, the family's standard of living had dropped sharply.  After young Ansel was dismissed from several private schools for his restlessness and inattentiveness, his father decided to pull him out of school in 1915, at the age of 12. Adams was then educated by private tutors, his Aunt Mary, and by his father. His Aunt Mary was a follower of Robert G. Ingersoll, a 19th-century agnostic, abolitionist and women's suffrage advocate. As a result of his aunt's influence, Ingersoll's teachings were important to Ansel's upbringing. During the Panama-Pacific International Exposition in 1915, his father insisted that, as part of his education, Adams spend part of each day studying the exhibits. After a while, Adams resumed and then completed his formal education by attending the Mrs. Kate M. Wilkins Private School, until he graduated from eighth grade on June 8, 1917. In his later years, he displayed his diploma in the guest bathroom of his home.

His father raised him to follow the ideas of Ralph Waldo Emerson: to live a modest, moral life guided by a social responsibility to man and to nature. Adams had a warm, loving and supportive relationship with his father, but had a distant relationship with his mother, who did not approve of his interest in photography.

Youth
Adams taught himself piano at age twelve. Music became the main focus of his later youth. Possessing an eidetic memory, he quickly learned to read music and play the piano. Soon he was taking lessons, and the ardent pursuit of music became his substitute for formal schooling. One of his childhood tutors was composer Henry Cowell. For the next dozen years, the piano was Adams's primary occupation and, by 1920, his intended profession. Although he ultimately gave up music for photography, the piano brought substance, discipline, and structure to his frustrating and erratic youth. Moreover, the careful training and exacting craft required of a musician profoundly informed his visual artistry, as well as his influential writings and teachings on photography.

Adams first visited Yosemite National Park in 1916 with his family. He wrote of his first view of the valley: "the splendor of Yosemite burst upon us and it was glorious... One wonder after another descended upon us... There was light everywhere... A new era began for me." His father gave him his first camera, a KodakBrownie box camera, during that stay and he took his first photographs with his "usual hyperactive enthusiasm".He returned to Yosemite on his own the following year with better cameras and a tripod. In the winter, he learned basic darkroom technique working part-time for a San Francisco photo finisher. Adams avidly read photography magazines, attended camera club meetings, and went to photography and art exhibits. With retired geologist and amateur ornithologist Francis Holman, whom he called "Uncle Frank," he explored the High Sierra, in summer and winter, developing the stamina and skill needed to photograph at high elevation and under difficult weather conditions.

Close-up of leaves In Glacier National Park (1942)
While in Yosemite, he had frequent contact with the Best family, owners of Best's Studio, who allowed him to practice on their old square piano. In 1928, Ansel Adams married Virginia Best in Best's Studio in Yosemite Valley. Virginia inherited the studio from her artist father on his death in 1935, and the Adams continued to operate the studio until 1971. The studio, now known as the Ansel Adams Gallery, remains in the hands of the Adams family.

At age 17, Adams joined the Sierra Club, a group dedicated to preserving the natural world's wonders and resources, and he was hired as the summer caretaker of the Sierra Club visitor center in Yosemite Valley, the LeConte Memorial Lodge from 1920 to 1924. He remained a member throughout his lifetime and served as a director, as did his wife. He was first elected to the Sierra Club's board of directors in 1934, and served on the board for 37 years, until 1971. Adams participated in the club's annual High Trips, and was later responsible for several first ascents in the Sierra Nevada.

During 1919, he contracted the Spanish Flu during the 1918 flu pandemic. Adams fell seriously ill but recovered after several months to resume his outdoor life.