A publicity campaign has been launched to highlight details of a new law allowing the first UK "gay marriages".
Nine EU countries have legally-recognised same-sex partnerships
The previous legal situation was described as "ridiculous" by deputy equality minister Meg Munn.
The Civil Partnership Act, which gives same-sex couples the same tax rights as heterosexual married couples, became law last November.
Gay couples will be able to tell register offices of their aim to form a civil partnership from 5 December.
A 15-day waiting period means that 21 December is the first day couples can tie the knot.
The deputy equality minister launched the publicity drive at Westminster Register Office in London, which has so far received more than 100 inquiries from gay couples.
The Act allows couples to sign an official document in front of the registrar and two witnesses.
Registration will only be available to homosexual couples and not as an alternative to heterosexual marriage.
The Act does not use the term "gay marriage" but closely follows a marriage contract. Partners will also be able to dissolve the agreement in the form of a divorce.
The partnerships will grant gay people next-of-kin rights in hospitals, and give them the benefit of a dead partner's pension and exemption from inheritance tax on a partner's home.
Ms Munn said: "It is ridiculous that we have had a system that does not recognise the relationship of a gay couple who may have lived together for 20 years.
"One partner could be excluded from the funeral if the other died, or lose their joint home because of inheritance tax."
Some gay rights groups have criticised the new law for stopping short of full marriage and for excluding heterosexual couples.
Some form of legally-recognised civil partnership already exists in nine other EU countries as well as in some states in the US and Australia.
Department of Trade and Industry officials estimate there will be more than 42,000 civil partnerships in the UK by 2050.
Some register offices have already been preparing for the law change, including Brighton Town Hall, where several couples have already signed up to marry on 21 December.