Over a period of forty years, from 1896 to 1935, Schenker maintained meticulously detailed diaries, a rich repository of information of all types. The diaries before 1912 are written in Heinrich's own hand, on a variety of sizes and formats of paper. After 1912 they were taken down, by dictation, in the hand of his companion (later wife) Jeanette in a consistent format: 9 x 11½ inches (23 x 29 cms), 25 lines per page, in minute handwriting. In all, they comprise 3,970 pages.

Abundant in biographical matter, they include information about Schenker's family, the fine detail of every-day life, domestic arrangements, daily appointments, professional schedules, meetings with friends (with summaries of conversations), medical conditions, purchases, payment of bills, etc. The reports of concerts, operas, plays, and exhibitions both attended and read about in newspapers (with critical reactions), and (later in life) of the radio programs and 78rpm recordings to which he listened, all these paint a vivid portrait of Viennese cultural life and Schenker's ever-pungent response to it. The diaries also chart the genesis and development of his published and unpublished writings, his dealings with publishers, authorities, attorneys, Viennese musical institutions and their officials, the performers and conductors of his day, and the workings of his private piano teaching studio.

Schenker took a keen interest in political and social matters. His reports (at first and second hand) mirror the course of European history as it unfolds through pre-war events, World War I, the inter-war years, and the rise of Nazism—all viewed from his unrepentantly German-nationalist standpoint. Paradoxically, he was a Jew who retained his allegiance to Judaism, and his portrayals of Jews in an anti-semitic Vienna are of great social-historical interest. He offers an "insider" account of the deprivations suffered by Viennese in the later war years and subsequent period of hyper-inflation. At the same time, he affords wonderful insights into the world of the Viennese coffee-house, with its gatherings, chance encounters, debates, and hard-fought negotiations.

Between September 1914 and the end of the war, Schenker made numerous entries about troop movements, battles, official diplomatic “notes” issued by various governments (especially with regard to the sinking of the Lusitania in 1915), newspaper articles, and the effect of the war on his own life and that of his friends and pupils. Between late November 1918 and early June 1919, however, he kept a separate, unnamed document in which he refers to all the newspaper articles he read on the political situation in Europe in the aftermath of Germany’s surrender. During this period, then, there are usually two diary entries, in separate manuscripts; to help readers distinguish between them, one of these is specifically marked “Political Diary.”