Questionnaires will be posted out to an estimated 26 million households across England and Wales today as the 2011 Census begins.
The survey documents will start to drop through letter boxes from tomorrow (March 8) in one of the biggest single mail outs the Royal Mail has handled.
Television adverts were broadcast from February 21 to raise public awareness of the impending Census Day on March 27.
The big counting operation will employ 35,000 field staff as advisers, co-ordinators, enumerators and census collectors collate data for the £482 million information-gathering exercise.
Householders will be asked a range of questions covering areas such as national identity, ethnic group, educational qualifications, job titles, travel-to-work method and state of health.
The census will include questions for the first time on civil partnerships, second homes and recent migration.
People born outside the UK will be asked when they most recently arrived in the country, with those who arrived in the past year asked how long they intend to stay.
There will also be a question asking people if English is their main language and how well they can speak it.
The census will gauge the extent to which carers provide support to family members, friends, neighbours or others suffering from long-term health problems or problems related to old age.
But there will be no questions on income, sexual orientation or nature of disability.
In 2001 - the first time a voluntary question was asked about faith - almost 400,000 people claimed their religion was "Jedi". This was in addition to almost 7,000 who said they were witches.
The 2011 Census will make use of technology and will invite respondents to complete their census forms online for the first time. There is also a census helpline for people with queries.
Organisers said the information from the once-a-decade exercise will be used by health authorities, councils and a range of other bodies to plan services.
It is also a source for research by future generations including historians, genealogists and academics.
The Office for National Statistics (ONS) said this year's census will be using a much improved address register.
It also insisted the information it gathers will be confidential for 100 years and not shared with other agencies such as the police or tax authorities.
2011 Census director Glen Watson said: "People should look out for the purple and white envelope landing on their doormat in the next two weeks.
"Once people get their form they can, if they prefer, fill it in online by going to http://www.census.gov.uk. This will be quicker and it's better for us because we won't need to scan the forms and decipher all that handwriting.
"Of course if people want, they can still do it by hand. Completing the census form promptly and sending it back to us means no one will have to knock on your door to remind you.
He added: "Census statistics enable the authorities in England and Wales to plan properly for the future for school places, housing, roads, emergency services and a host of other local services."
However, critics of the 2011 Census have argued it is not only an infringement of civil liberties, but unnecessary, as many authorities already have most of the information about citizens.
Filling out the census is compulsory, with the threat of a fine of up to £1,000 if a questionnaire is not completed and returned.
However, only 38 people were convicted for not filling out the census last time after the ONS reported a little over 100 people to the Crown Prosecution Service.
The first information from the 2011 Census is expected to be released in 2012, consisting of population estimates by age and sex for each local authority area, with more detailed statistics released in 2013.
The census this year is the biggest ever conducted but could also be the last.
An ONS working group is looking at future arrangements 'Beyond 2011'. A report is due to go to ministers and the Government to decide its future.Reuse content