The Marcus Lester Aaron Correspondence collection primarily contains letters written from Aaron to his parents in Pittsburgh during his four years as an undergraduate at Princeton University from October 9, 1916 to June 9, 1920. Aaron wrote daily letters to his parents and sister during his years at Princeton, thereby providing a continuous record of the four years. The letters include various enclosures, such as clippings, concert programs and grade reports.

The 1916-1918 letters deal with the effect of the war on campus. The January 1917 letters mention the possibility of war. In March, voluntary outdoor war drills begin and in November the Undergraduate Student Council makes drills mandatory. The drills eventually incorporate wearing uniforms, bayonets and trench digging. In November 1917, Aaron receives a letter from a friend serving with the American Expeditionary Force in France. Other wartime topics include: friends seeking officer status; drills continuing through exams; Memorial Day celebration; marching with the Naval Reserve, aviators, and members of battalion; and interaction with the Princeton Aviation School.

Aaron first refers to being Jewish in January 1917 when he states that 2% of his class is Jewish. He suggests discrimination in his October 24, 1917 letter: he talks about applying to the International Polity Club but not getting in because of being Jewish. From February to May of 1918 he makes a handful of references. He also mentions being excused from class for Jewish holidays, and increasing Jewish membership in Phi Beta Kappa. Other recurring topics in the letters include writing for The Prince, P-rading around campus and the town with fellow students, attending concerts and lectures, football games, working in the history lab, and membership in Phi Beta Kappa.

After 1919, the letters focus on Aaron's experience as a Jewish student and his involvement in the creation of the first Jewish student organization on campus. In December 1919, Aaron begins to formulate plans for a Jewish Congregation at Princeton; and in a letter to Rabbi Louis Egelson, Aaron outlines the Congregation's purpose and administrative structure. In January 1920, the Congregation begins meeting and holding services. In March 1920, Aaron makes specific references to discrimination by eating clubs towards Jewish students. Aaron remarks on his frustration with his fellow Jewish students, who he believes are afraid of their own religion and unwilling to openly practice. It is notable that Aaron believes Princeton as a community to be "not only willing that we should worship in our way with the fullest possible freedom, but…willing to give us absolutely all the help—official and personal—that they can" (May 18, 1920 letter). Despite Aaron's doubts, attendance at the congregation's services steadily increases (Aaron and Meyer successfully engage the renown Rabbi Stephen Wise to speak at Princeton in the spring of 1921), and the organization proves durable as documented in the post-1921 exchanges between Morton Meyer and Aaron.

A small number of documents dating before October of 1916 include: college entrance exam results and his Princeton acceptance letter. Materials dating after Aaron's graduation include: five letters sent to Aaron from Morton Meyer of the Jewish Congregation, an official "Jewish Group of Princeton" letter, and a 1923 letter from the Congregation. Other enclosed papers include Aaron's acknowledgement of academic credit, report cards, commencement pamphlets, university papers, clippings from The Daily Princetonian, some with articles written by Aaron, a signed letter of request to use Aaron's dormitory room from President Hibben, and a signed note from Sergeant Major H.H. Undong. Important occurrences Aaron mentions are the measles outbreak at Princeton in May 1917, the October to December 1917 coal shortage, and the May 1920 fire at Princeton.