Sending preprints and translation of work on results obtained with Landau. Appendix 1: L Landau, A Abrikosov, I Khalatnikov, On the quantum theory of fields, 29 pages. Appendix 2: A Abrikosov, I Khalatnikov, Utilization of two limiting moments in field theories, 8 pages. Appendix 3: I Pomeranchuk, Vanishing of renormalized charge in quantum electrodynamics, 15 pages. Appendix 4: I Pomeranchuk, Renormalisation of the meson charge pseudoscalar coupling, 6 pages. Appendix 5: I Pomeranchuk, On the vanishing of the renormalized meson charge in pseudoscalar theory with pseudoscalar coupling, 11 pages.

This letter gives the results of Blokhintzev's calculations on the wave equation of a field interacting with heavy particles.

Ivanenko writes of a letter he received from Heisenberg about his participation in the non-linear spinor theory of matter. He mentions some papers published by himself and his associates dealing with non-linear theories.

Landau has heard from Weisskopf about Pauli's and Heisenberg's theory and would like to know more about it.

Landau agrees with Pauli on Heisenberg's theory. He makes remarks on Lee's model and future theory.

Yoffe thinks that Thirring's cut-off method is wrong.