A theoretical physicist at Cambridge, Douglas Hartree is best known for his work in numerical methods and the machines that could be used to calculate them with increasing speed and sophistication.This reprint of Hartree's principal work also includes his inaugural Cambridge lecture, Calculating Machines: Recent and Prospective Developments and Their Impact on Mathematical Physics, which is extremely difficult to obtain and which makes ideal preliminary reading for the main set of lectures presented in Calculating Instruments and Machines. In these, Hartree provided the first comprehensive survey of the significant developments in computation that were going on at the time-the main directions of development in storage systems, serial machines, and parallel programming and coding, and particularly with high-speed automatic digital machines that were precursors of the modern stored program computer.Calculating Instruments and Machines was originally published in 1949 by the University of Illinois Press. It is Volume VI in The Babbage Institute Reprint Series.