The ARGO-YBJ experiment was installed in the Tibet region of China, 4300 meters above sea level. It run continuously from November 2007 until February 2013, with the goal of observing astronomical $\gamma$-ray sources in the energy range between a few hundred GeV and about 100 TeV, and primary cosmic rays in the energy range between about 1 TeV and a few PeV. The unique feature of the ARGO-YBJ detector was its full-coverage layout of Resistive Plate Chambers on an area of (78 x 74) m$^{2}$, with a guard ring around and a full area of 11000 m$^{2}$. The most important results obtained by ARGO-YBJ will be presented, with specific focus on the observation and monitoring of galactic and extragalactic $\gamma$-ray sources and primary light-nuclei spectrum and knee.