Egypt's Christian leaders have neither come out for or against the constitution, but instead encouraged believers to vote their own conscience.
A controversial edict
The rocky road to the referendum began when judges threatened to shut down the assembly tasked with drafting the constitution.
President Morsy then issued an edict in late November declaring all of his past and present decisions immune from judicial review until the holding of the constitutional referendum.
He also sacked the head of the judiciary. The judicial system has many in its ranks who are loyal to former autocratic President Hosni Mubarak.
The Islamist president's opposition saw the exceptional move as a grab for dictatorial powers and poured into the streets, converting Tahrir Square in central Cairo back into the center of public discontent it had been during the uprising that brought down Mubarak.
The president has since dropped his provocative decree going forward, but the situation has remained tense, and violence has continued.
Morsy's Islamist allies rushed the drafting of the constitution to completion, which some saw as a tactic to allow him to drop his controversial edict more quickly. Others feared it to be another grab for power. Non-Islamist assembly members quit the process, which served to increase suspicion against the Islamists.
The outcome of the election and the unrest associated with it are important to the stability of volatile North Africa and the Middle East -- where Egypt is a key player -- and the situation is being watched closely around the world.