The Syrian opposition was an umbrella term for the Syrian revolutionary organizations that opposed Bashar al-Assad's Ba'athist regime during the Syrian Revolution and Syrian civil war. The opposition factions in Syria became active as grassroots movements during the mass demonstrations against the Ba'athist regime. The Free Syrian Army (FSA) was the most prominent armed revolutionary group in the initial stages of the war; but it declined and became decentralized by 2015. By 2021, Hay'at Tahrir al-Sham (HTS) had become the strongest armed faction within the Syrian opposition.
In July 2011, as the situation turned into a civil war, defectors from the Syrian Armed Forces formed the Free Syrian Army. In August 2011, dissident groups operating from abroad formed a coalition called the Syrian National Council. A broader organization, the Syrian National Coalition (SNC), was formed in November 2012. Although the groups based abroad established contact with those in Syria, the Syrian opposition suffered during the whole conflict from infighting and a lack of unified leadership, as well as lack of foreign aid as the war became deadlocked.