Scotland has banned parents smacking their children, becoming the first part of the UK to do so.
Scotland becomes the 58th country to outlaw corporal punishment after the defence of justifiable assault was removed from Scots law.
Parents and carers were previously allowed to use physical force to discipline their children if it was considered "reasonable chastisement".
The new law seeks to give children the same protection from assault as adults. Wales is also expected to follow suit with the introduction of a ban by 2022.
Sweden was the first country in the world to ban smacking in the home when it outlawed corporal punishment in 1979.
Children's charity the NSPCC said Scotland's ban was a "common sense" move.
Joanna Barrett from the NSPCC said: "This law sets out in clear terms that physical punishment should no longer be part of childhood in Scotland and it marks a momentous step in making it a country where children's rights are truly recognised, respected and fulfilled."
The Scottish Green MSP John Finnie, who introduced the changes, said smacking teaches children that "might is right", and that the ban would "send a strong message that violence is never acceptable in any setting".
He said: “As I have progressed my campaign over the last four years, it has been noticeable just how many people believed that striking a child was already outlawed.
“I am pleased that this will now be the case.”
Scotland children’s minister, Maree Todd, said: “I’m very pleased that Scotland has become the first part of the UK to legislate to ensure that children, without exception, have the same protection from assault as adults.
“This outdated defence has no place in a modern Scotland. It can never be reasonable to strike a child.”
Prior to this decision, regarding whether the chastisement of a child under 16 was reasonable, the courts took into account factors such as the nature of the punishment, its duration and frequency, the age of the child and the effect - both physical and mental - it had on them.
The bill will end the defence of "reasonable chastisement", meaning parents could face prosecution for any use of physical punishment on their children.
The act uses the same definition of physical punishment, sometimes referred to as corporal punishment, used by the UN Committee on the Rights of the Child.
The Liberal Democrat MSP Alex Cole-Hamilton said he was “delighted” about the change to the law.
He said: “The abolition of this Victorian-sounding legal defence is long overdue.
“It is backed by countless studies and experts from the children’s commissioner to police officers, social workers, nurses, and children’s and parenting charities.
A report published by a group of Scottish children's charities in 2015 found that the physical punishment of children was more common in the UK than in similar countries such as the US, Canada, Italy, Germany and Sweden.
The researchers estimated that between 70% and 80% of parents in the UK had used physical punishment, with children aged between three and seven the most likely to be smacked.
They also found that many parents did not view smacking as a "good thing", but believed that sometimes it was the "only thing that will work".
Campaign group Be Reasonable Scotland, which opposed the legislation, warned that “even the mildest physical discipline will be treated as abuse” and could lead to parents being prosecuted.
A spokesman for the group said: “In the years ahead, loving parents who have had no contact with the authorities previously and who present no risk to their children will face stressful intervention, blacklisting on police databases and even criminal records for smacking.
Parents in England and Wales can currently face criminal charges if they hit a child so hard that it leaves a mark, or causes bruising, swelling, cuts, grazes or scratches.