Boulanger returned to Paris in January 1946, joyfully reuniting with friends in France while painfully separating from those back in the United States. Boulanger's letters provide a glimpse of life in Paris in the immediate postwar years. She writes of the lack of heat in her apartment, during the middle of one of Europe's coldest winters in years (January 27, 1946). In April 1946, Boulanger references purchases acquired through the black market (April 27, 1946). Here, she briefly describes how difficult it was to carry out daily activities and the bravery of those who attempted to meet people's needs through illegal measures. And yet, although Boulanger's optimism outshone the inconveniences of her reality initially, her outlook began to sour by 1950, amid the uncertainties brought about by the onset of the Cold War. Indeed, by fall of 1950, her optimism had turned to anger, as she wrote to Stravinsky on September 14, 1950: “I cannot hope that you’ll come to Europe, a Europe that everything threatens. What savages, what fools we are who, no matter what, want to find nothing more than perfect ways to destroy everything.” Boulanger's letters bear witness to the extensive postwar struggle to establish normalcy on the unstable continent.

This fragile reality framed Boulanger's efforts as a critic, performer, and lecturer as she worked aggressively to rebuild European artistic traditions. Upon her return, Boulanger gave numerous lectures, wrote criticism, and traveled regularly to places both familiar—such as London, England—and uncharted, such as Bryanston, England, and Solesmes, France. She threw her energy into lectures and performances of Stravinsky's works that were still unknown to many Europeans. She lectured extensively, imploring Europeans in general and Parisians in particular to engage with the high neoclassical output of her beloved composer. Her talks, mentioned in numerous letters, overflowed with personal anecdotes and stories collected during her frequent visits with the Stravinskys in California. Whenever possible, Boulanger, along with the help of Soulima and Jean Francaix, performed Stravinsky's wartime compositions in the form of two-piano transcriptions. One of the most fascinating of all her performance engagements involved her conducting the Symphony of Psalms in Brussels no less than seven times in four days (September 15, 1950).