Källén writes about his work on quantum electrodynamics and especially about renormalization.

Källén writes on an interim report on his work on quantum electrodynamics.

Källén criticizes Thirring's remarks about his theory communicated by Pauli.

Källén replies to two letters and questions about dipole ghosts. He talks about his own work.

Källén writes to Pauli from CERN and gives the results of his calculations on the probabilities of dipole states.

Källén replies to Pauli about his difficulties as regards the S-matrix.

Källén writes of the result of his calculation of the splitting of a dipole state in the presence of an additional N-particle.

Källén comments on the paper by Heisenberg and Haag. He writes on Wightman's axioms.

Källén has difficulties in understanding Pauli's last letter. He talks about rumours regarding the discovery of spin in $\Pi^{+}$-mesons.

Källén talks about Heisenberg's claim that the states in the Hilbert-space I possess a positive norm.