Dyson writes about the renormalization method in quantum electrodynamics, especially on the renormalization of the Heisenberg operators.

Dyson explains why the symmetrical treatment of the radiation field gives the right answer in Schwinger's theory. The letter contains information about experimental results of Powell on fast Pi-mesons and a discussion of the question longitudinal photons.

Dyson writes about Baranger's calculation of the relativistic correction to thesecond order lamb-shift. He adds to the letter his ideas about the renormalization programm.

Dyson sends more details about the renormalization method.

The letter contains Dyson's reply to Pauli's letter about the convergence problem, meson theories and renormalization and series expansion.

Peierls offers a proof of the Jacobi identity, and reports on progress in his work on non-local field theories,which includes finding a method which leads to reasonable solutions of the action principle.

Peierls refers to the Møller-Kristensen theory. He says that the difficulties with their theory may arise from discontinuities in the form factor.

Peierls replies to two letters by Pauli. He comments Pauli's calculations as regards the non-local field theory, and on his view about the use of form-factors which may destroy the gauge invariance.

Peierls replies to Pauli's comments on his theory.