The Palestinians are preparing for their first census in a decade and hope the results will help them in peace talks with Israel.
Later this week, some 5,000 census-takers will fan out across the West Bank and the Gaza Strip, first to count buildings, and, in December, to count people. Results are expected by February.
"We hope we can use these statistics in the negotiations," said Palestinian negotiator Saeb Erekat, a supporter of moderate Palestinian President Mahmoud Abbas. "It's not only important for the political process, but also for building the institutions of the state."
Rapid Palestinian population growth would bolster Palestinian territorial demands, while Israelis' fear of being outnumbered in areas they control might make them more willing to consider a West Bank withdrawal.
The militant group Hamas, which controls the Gaza Strip, has also said the census results are important and that it will co-operate.
The first Palestinian census, conducted in 1997, counted 2.89 million Palestinians in the West Bank, Gaza and east Jerusalem, the territories Israel captured in 1967. According to estimates by the Palestinian Central Bureau of Statistics, the figure now stands at 3.9 million.
Some Israeli critics have dismissed the 1997 figures and current projections as inflated, a charge denied by Palestinian census officials.
Palestinians have one of the highest birth rates in the world, forcing Israel to consider the possibility that Jews, despite Jewish immigration, will one day be a minority in historic Palestine, the area between the Jordan River and the Mediterranean.