Scope and Contents: The main content of this collection are two sets of letters, written from Europe by physicist Robert Bruce Lindsay (RBL) to his parents, Robert and Eleanora Lindsay, in New Bedford, Massachusetts. The first set was written in connection with RBL's and his wife Rachel's stay in Copenhagen between August 1922 and August 1923. The majority of these letters were written from Copenhagen while RBL was studying at Niels Bohr's Institute of Theoretical Physics. There are only fleeting references to the substance of RBL’s physics research (the most technically detailed letter is that of 17 June 1923, specially written to his father alone), but there are many glimpses into the personalities of the scientists with whom RBL came into contact, and lively descriptions of the experiences of two rather innocent young Americans on their first encounter with Europe. In addition to RBL's letters (scanned original letters and transcriptions) from Copenhagen, Folder 1 contains Rachel's letters during the couple's travels in Germany after the stay in Copenhagen published in the newspaper Newport Daily News. Folder 2 contains the second set of letters (transcriptions only) written during a second trip to Europe in 1937. It also contains transcribed extracts from RBL's diary and an introduction and epilogue by David Lindsay Roberts. Folder 3 contains autobiographical and biographical data on RBL. We are grateful to David Lindsay Roberts, the grandson of RBL, for sharing the material and allowing us to publish it.