Relativity principles and theories from Galileo to Einstein Motion is always relative to some thing. Is this thing a concrete body like the earth is it an abstract space or is it an imagined frame Do the laws of physics depend on the choice of reference It there a choice for which the laws are simplest Is this choice unique Is there a physical cause for the choice made These questions traverse the history of modern physics from Galileo to Einstein. The answers involved Galilean relativity Newtons absolute space the purely relational concepts of Descartes Leibniz and Mach and many forgotten uses of relativity principles in mechanics optics and electrodynamics until the relativity theories of Poincaré Einstein Minkowksi and Laue radically redefined space and time to satisfy universal kinds of relativity. Accordingly this book retraces the emergence of relativity principles in early modern mechanics documents their constructive use in eighteenth and nineteenth century mechanics optics and electrodynamics and gives a well rooted account of the genesis of special and general relativity in the early twentieth century. As an exercise in long term history it demonstrates the connectivity of issues and approaches across several centuries despite enormous changes in context and culture. As an account of the genesis of relativity theories it brings unprecedented clarity and fullness by broadening the spectrum of resources on which the principal actors drew