Questionnaires are to be posted out to an estimated 26 million households across England and Wales as the 2011 Census begins.
The survey documents will start to drop through letter boxes from Tuesday 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.
