The Order, published in the Gazette on 16 October 2020, provided statutory backing for the conduct of the 21C.

[1] The 21C comprised a simple enumeration on about nine-tenths of households in Hong Kong to provide basic information (e.g. year and month of birth and sex) and a detailed enquiry on the remaining one-tenth on a broad range of demographic and socio-economic characteristics.

Two slogans were adopted to promote the importance of the 21C and encourage households to use online questionnaires: 2021 Census: Provide Data for Hong Kong's Future Online Census: Convenient, Secure and Green Two mascots were also created to help disseminate publicity messages to the public, "Paul", and "Charlotte".

Besides, for households residing on fishing boats, their number was estimated based on aerial photos of all anchorages in Hong Kong Waters and their characteristics estimated based on information provided by the Agriculture, Fisheries and Conservation Department.

In light of the COVID-19 epidemic, C&SD had encouraged households to provide data through online questionnaire or telephone interview so as to reduce face-to-face contact.

[5] C&SD conducted the Pilot Survey for the 21C from 23 June to 4 August 2020 to test the questionnaire design and the operational arrangements for the 21C.