At the suggestion of his father, JQA begins a diary when he is twelve years old. Continuing the practice for the next sixty-eight years, he is one of the few American presidents to keep a diary while in office. For twenty-six of his journal-writing years, from January 1, 1795, until May 6, 1821, he records his thoughts each and every day in full entries; during other periods, he provides only short entries or notes for some days. Occasionally, towards the end of his life, he fails to make an entry, with the largest gap being four months (November 1846–March 1847).

JQA's diaries display the progression of his handwriting as an adolescent as well as his declining ability to hold a pen in old age. He records events, trips, discussions with pivotal people such as Thomas Jefferson and Henry Clay, and his evolving views on the important issues of his day, ranging from American independence to the abolition of slavery.

The diary entries in this section were written when JQA was twelve and thirteen years of age.