Solid state physics is the study of solids using the tools & techniques of quantum mechanics, statistical mechanics, electromagnetism, metallurgy, and crystallography. In the present manuscripts, Feynman considers various aspects of this field of study, including the Shockley experiment, cyclotron resonance, electrical conductivity, lattice defects, semi-conductors, impurities, solar cells, lasers, rectifiers & transistors, free electron gas, tunnel diodes, forces on electrons, and more.  While some of the papers appear to span from his early days as a professor at Cornell, the majority are likely lecture notes for courses he taught at Caltech in the mid-1960s.  This archive is best considered as the inspired legacy of his 1950's commitment to this subfield, which is most closely allied to electrical engineering aspects girding the advent of the modern computers, but also provides a kind of parallel track to Feynman's sustained commitment to coding.  It speaks directly to his desk-top copy of Kittel- (see lot 84), the classic tome on the subject.