We come together to commemorate the life of Shneior Lifson, a close friend to many of us, a magnificent human being, a great scientist with a lucid analytical mind and a towering personality. He had a cheerful character, with a good sense of humor, a sharp capacity for observation, an immense curiosity—directed mainly to science, culture, and ethical values. Almost to his last day, I saw him coming to his office on his bicycle. I was happy to see him, but also much moved to see that he could do it by bicycle. Our friendship started in 1950 when I joined the Institute as a Ph.D. student with Ephraim Katchalski-Katzir). Shneior was a Ph.D. student at the Weizmann Institute with his brother Aharon Katzir since 1949. There were the unforgettable, long evenings with the Katchalski-Katzir brothers—teaching seminars that included courses on vectors, tensors, and Hamiltonians, which for me were the only contact with these notions, and discussions on polyelectrolytes and proteins, as well as their synthetic models, the poly-α-amino acids. When the Institute built some apartment houses at the time I was going with my family for a postdoctoral period with the late Chris Anfinsen at the National Institutes of Health, we asked the Lifsons to participate on our behalf in a lottery for apartments. We wanted to live on the same floor as next-door neighbors. This actually materialized. I remember evenings with Shneior sitting on the floor playing his beloved eucharina, in a joyful atmosphere. On my return from the NIH, I also started collaborating with Shneior, which resulted in our only joint publication. This I would like to describe to you now. During my stay with Chris Anfinsen in Bethesda in 1956–1957, we discovered that when ribonuclease was stored with all 4 disulfide bridges reductively opened, with time all the enzymatic activity reformed.1 When I returned, I asked Shneior to help with the statistical analysis of the probabilities of reformation of activity of proteins upon reoxidation of the products of the reductive cleavage of disulfide bridges in these proteins. This effort resulted in the paper, “On the Reformation of Disulfide Bridges in Proteins,” published in 1959.2 In the case of RNase, the 8 cysteines could have reoxidized in 105 ways. Apparently, only one of them was actually reformed with all its enzymatic activity. Shneior Lifson did not shrink from public activities. At the Weizmann Institute he was Chairman of its Scientific Council, Head of the Department of Chemical Physics, and between 1963 and 1967 Director of the Institute. He was instrumental in creating the Open University and served as its first President. Shneior was an active member of the Pugwash Movement. He participated in many meetings, and had most interesting and illuminating, if sometimes frustrating encounters both with Arab and Russian scientists. For many years Shneior Lifson was interested in the origin of animate matter, and with his wife, Hanna, developed a model for prebiotic replication: Survival of the Fittest vs Extinction of the Unfittest.3 His last paper, again with Hanna, appeared after he passed away. Its title was “Coexistence and Darwinian Selection among Replicators.”4 One cannot talk about Shneior without mentioning his humor, and the wonderful way in which he told anecdotes. One of them I will always remember and that reminds me of Shneior is about the man who cannot fall asleep and his wife asks him why he cannot sleep. He answers that he owes their neighbor a thousand dollars, which he has to return the next morning, and he does not have the money. His wife immediately knocked on the neighbor's door. When he opened the door, she asked him whether her husband owes him the thousand dollars. When he replies that her husband does indeed owe him a thousand dollars and must return the money the next morning, she tells him that her husband will not repay him. Returning to her husband, she says: “Now you can sleep. Our neighbor will not sleep.” We will all remember Shneior as a cheerful person, a delightful friend and a man with a great mind.