Events at the beginning of the 21st century have brought a fundamental change to the security environment in the Kingdom of Saudi Arabia of a significance not witnessed in the region since the Iranian Revolution in 1979. The fall of Saddam Hussein's regime in 2003 eliminated the most significant external threat facing Saudi Arabia. At the same time, internal threats to the Kingdom appear to be increasing. The demographic and economic challenges facing the Kingdom are contributing to internal instability. Increased instances of political violence, particularly suicide bombings against targets within the Kingdom, have been carried out by terrorists linked to al-Qaeda. These attacks have targeted Westerners and, for the first time in May 2003, non-Saudi Muslims. This paper examines the security challenges facing Saudi Arabia at the start of the 21st century. It argues that while external threats to the Kingdom remain, the greater threat to security may lie within the Saudi state: the result of a failure to address current political realities. Major security challenges include the threat from Iran, economic and demographic pressures, the question of succession within the ruling al-Saud family and maintaining the U.S.- Saudi security partnership, a relationship which has endured over 50 years.