Bell Labs in the 60's and input-output stability

During the 1960s at Bell Labs the author knew some of the superstars who contributed to the field of electrical engineering (e.g., Bode, Darlington, and Shannon). One purpose of the paper is to describe the intellectual environment at Bell Labs and some of the author's interactions with these individuals. Another purpose is to describe the origins of input-output stability theory (i.e., of extended spaces, the small-gain theorem, the passivity theorem, the circle criterion, etc.), and the impact of the books available then on functional analysis, integration theory, and the theory of Fourier transforms.