  The Auger Engineering Radio Array (AERA) complements the Pierre Auger
Observatory with 150 radio-antenna stations measuring in the frequency range
from 30 to 80 MHz. With an instrumented area of 17 km$^2$, the array
constitutes the largest cosmic-ray radio detector built to date, allowing us to
do multi-hybrid measurements of cosmic rays in the energy range of 10$^{17}$ eV
up to several 10$^{18}$ eV. We give an overview of AERA results and discuss the
significance of radio detection for the validation of the energy scale of
cosmic-ray detectors as well as for mass-composition measurements.
