In the four or so decades since the creation of Iran’s Islamic Republic, the ruling regime has faced numerous challenges from its restive population. The “Green Revolution” in 2009, which many observers regarded as a precursor to the so-called Arab Spring that followed two years later, is still regarded as the most serious attempt to force the regime to undertake wholesale reform.

Mass protests are spreading across Iran, but what's driving them and where could they lead? Here's what we know.

Ailing economy sparks biggest uprising in years, with protesters saying it’s time to hit regime when it’s at its weakest