The 2021 census takes place next month, with everyone in England and Wales expected to take part.
For the first time, the census - which happens every 10 years - will be 'digital first', with people encouraged to take part online.
It will also include a voluntary question for the first time on whether someone's gender is the same as their sex registered at birth.
But what is the census and how does it work?
What is the census and when does it happen?
The census is a survey that takes place every 10 years, providing a snapshot of all the people and households in England and Wales. The first census was in 1801 and the most recent in 2011.
Run by the Office for National Statistics (ONS), the information it provides is used to help plan and fund public services, including transport, education and healthcare.
The next census in England and Wales is due to take place on March 21, 2021.
A practice-run took place in 2019 to make sure all the systems worked.
Censuses in Scotland and Northern Ireland are run by National Records of Scotland and the Northern Ireland Statistics and Research Agency.
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Do I have to take part in the census?
The Census Act 1920 makes it compulsory for everyone in England and Wales to take part in the census and answer the questions.
However, the Census (Return Particulars and Removal of Penalties) Act 2019 amended the law to allow new questions on sexual orientation and gender identity to be voluntary in future censuses. The same step was previously taken to make questions on religion voluntary.
Why is the census important?
Information from censuses is always used to understand society and what it needs in terms of services.
The ONS said it has used information from past censuses to help understand how the COVID pandemic has affected people in different ways.
The 2021 census is likely to give new information to better understand how the pandemic has affected society and also to make sure that services like hospitals, schools and universities continue to meet the needs of society as it changes.
How will the 2021 census work?
For the first time, the 2021 census will be 'digital-first' to help keep in line with government guidelines.
That means people will be encouraged to respond online using devices including mobile phones and tablets, with help available by phone, web chat, email, social media or via text.
If it's within government guidelines, the ONS will also open Census Support Centres to help people fill in their online questionnaire.
After Census Day, at the end of March and into April, special census field officers will be visiting households who haven't completed a census form to encourage them to complete one.
The ONS says the field officers will work in the same way as a "postal or food delivery visit", wearing full PPE and will never set food in your home.
What happens to the information you give to the census?
Overall results from the census are usually available the following year, but no individual person is identified in the statistics the ONS published.
All personal records are locked away securely for 100 years and only then will future generations be able to see them.
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