The article discusses the relationship between L. P. Karsavin and S. L. Frank. Cooperation between them started in Russia and was continued in emigration. In particular, they worked together at the Russian Religious-Philosophical Academy and the Russian Scientific Institute in Berlin and they both participated in the Russian Christian student movement. They not only participated in scientific, pedagogical and publishing projects, but also helped each other in various personal matters. Karsavin engaged Frank to some Eurasian publications, despite the fact that the latter did not belong to the Eurasians. The Bakhmeteff archive at the Columbia University contains five letters from Karsavin to Frank and one letter to his wife, Tatyana Sergeevna, as well as two letters of Karsavin’s wife Lydia Nikolaevna to Frank’s wife Tatyana Sergeevna, which are published in this issue of the journal. The letters reveal the history of personal and creative relationships between the two philosophers. Beside it, the text “In the Memory of Lev Platonovich Karsavin”, the original of which is also kept in the Bakhmeteff archive, is also published. These archival materials help us better understand the creative work of Frank and Karsavin as well as some details of their philosophical biographies.