The great Islamic pilgrimage to Mecca, Saudi Arabia, named the Hajj, is one of the largest pilgrimages in the world. Besides the Islamic creed, daily prayers, almsgiving, and fasting during Ramadan, the Hajj is one of the five pillars of Islam. It is a religious duty: every able-bodied Muslim is obliged to make the pilgrimage to Mecca at least once in her/his lifetime. In 2009 more than three million pilgrims approached Mecca to perform Hajj. Most of the rites performed by the pilgrims during the Hajj are related to important incidents of the life of Abraham. They are performed at certain places in Mecca and the region east of Mecca. In the past decades several severe stampedes with hundreds of casualties have occurred. One of the most dangerous rituals is the stoning of the devil at the Jamarat Bridge in the Mena valley. Since 2000 there has been increased, ongoing improvement of the infrastructure of the locations of rites (particularly the Jamarat Bridge) at the operational level. These improvements aim to avoid crowd disasters by modern crowd-control measures. This chapter outlines some of these improvements.