| How solar flares accelerate electrons up to relativistic energies is one of the main unsolved problems in Heliophysics. Remote sensing at radio and hard X-ray wavelengths provide crucial diagnostics of flare-accelerated electrons in the solar corona. In-situ observations in interplanetary space give direct observations of flare-accelerated electrons escaping the Sun. In this review, recent results combining these observations are discussed, with a special emphases on future observations with Solar Orbiter and Solar Probe +. |