some key facts about the election:
An alley of Peshawar city is decorated with campaign banners for the upcoming election in Peshawar, Pakistan. AP Photo
There are 4,670 candidates standing for 272 seats in a first-past-the-post system in the 342-member lower house.
Sixty seats reserved for women and 10 for non-Muslim minorities are distributed by proportional representation based on the parties' share of the directly elected seats.
A total of 10,955 candidates are running in elections for Pakistan's four provincial assemblies in Punjab, Sindh in the south, Khyber Pakhtunkhwa in the northwest and Baluchistan in the southwest.
Only 161 women are standing for the national assembly, 3.5% of the candidates.
There are 86.2 million registered voters -- 37.6 million women and 48.6 million men.
The Election Commission has set up around 70,000 polling stations, 40% of them for women, to be staffed by more than 600,000 people.
Voters must present their ID cards and their fingers are inked after voting.
HOURS OF VOTING
Polls will open at 8:00 am (0300 GMT) and are scheduled to close at 5:00 pm.
Elections have been postponed in three constituencies -- two for provincial assembly seats and one for a national assembly seat -- after candidates were assassinated during the campaign.
More than 600,000 security personnel, including 50,000 soldiers, will be deployed during the election to guard against Taliban attacks that have killed more than 100 people during the campaign.
Pakistan's seven semi-autonomous federally administered tribal areas elect 12 members to the national assembly.
This year is the first time that political parties have been able to contest the election in the area, a Taliban and Al-Qaeda hotbed on the Afghan border.
Ballots will be counted by hand at individual polling stations. They will be forwarded to provincial election commission offices and then tallied in Islamabad.
First results are expected from 10:00 pm.
The election commission will certify final results within a week.
A majority of 172 out of 272 directly elected seats is required to form a government.
Tens of thousands of local and international observers, along with representatives of the candidates and media, are to monitor polling. The main Pakistan observer organisation is the Free and Fair Election Network, which aims to field 43,500 observers.