Facebook and Twitter face being made to pay for action to tackle the "undeniable suffering" the internet can cause, the Culture Secretary has announced.
Cyber-bullying, trolling and under-age access to porn will be targeted in plans drawn up by Karen Bradley to make the online world safer.
Social media companies will be hit by an industry-wide levy to fund measures to deal with online harm.
A new code of practice to tackle bullying, intimidating or humiliating online content would be also be created.
Mrs Bradley said: "The internet has been an amazing force for good but it has caused undeniable suffering and can be an especially harmful place for children and vulnerable people.
"Behaviour that is unacceptable in real life is unacceptable on a computer screen.
"We need an approach to the internet that protects everyone without restricting growth and innovation in the digital economy.
"Our ideas are ambitious - and rightly so. Collaboratively, government, industry, parents and communities can keep citizens safe online, but only by working together."
The proposals outlined in the Internet Safety Green Paper also include an annual internet safety transparency report to keep tabs on online abuse.
Support would be given to digital start-ups to make sure they build safety features into new apps.
The government also confirmed plans announced earlier this year to make relationship lessons, which will include online safety, compulsory in schools.
It highlighted research from the UK Safer Internet Centre that found 64% of 13-17-year-olds have seen people posting offensive images or videos.
Centre director David Wright said: "As the national centre dedicated to making the UK the safest place in the world to be online, the UK Safer Internet Centre, a partnership of three charities - Childnet, the Internet Watch Foundation and South West Grid for Learning - welcomes any piece of work that helps deliver this objective.
"Technology plays a fundamental role in everyone's lives presenting both opportunities and threats.
"Our aim is to promote national collaboration around these issues to deliver positive change among children and young people, and those who support them, through education and increased awareness of the safe and responsible use of technology."