Incest
Aunts, uncles, nieces or nephews

In the Netherlands, marrying one's nephew or niece is legal, but only with the explicit permission of the Dutch government, due to the possible risk of genetic defects among the offspring. Nephew-niece marriages predominantly occur among foreign immigrants. In November 2008, the Scientific Institute of the Christian Democratic Party (CDA) announced that it wanted a ban on marriages to nephews and nieces.

Consensual sex between individuals aged 16 and older is always lawful in the Netherlands and Belgium, even among closely related family members. Sexual acts between an adult family member and a minor are illegal, though they are classified not as incest but as abuse of the authority such an adult has over a minor, comparable to that of a teacher, coach, or priest.

In Florida, consensual adult sexual intercourse with someone known to be one's aunt, uncle, niece, or nephew constitutes a felony of the third degree. Other states also commonly prohibit marriages between such kin. The legality of sex with a half-aunt or half-uncle varies state by state.

In the United Kingdom, incest includes only sexual intercourse with a parent, grandparent, child, or sibling, but the more recently introduced offense of "sex with an adult relative" extends as far as half-siblings, uncles, aunts, nephews, and nieces. However, the term 'incest' remains widely used in popular culture to describe any form of sexual activity with a relative.

In Canada, marriage between uncles and nieces and between aunts and nephews is legal.
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