Exploring the foundations of the physical universe with space tests of the equivalence principle.

We present the scientific motivation for future space tests of the equivalence principle, and in particular the universality of free fall, at the 10^{− 17} level or better. Two possible mission scenarios, one based on quantum technologies, the other on electrostatic accelerometers, that could reach that goal are briefly discussed. This publication is a White Paper written in the context of the Voyage 2050 ESA Call for White Papers. [ABSTRACT FROM AUTHOR]