Protests are taking place across India against rising attacks on Muslims and Dalits (formerly untouchables) by vigilante cow protection groups.
About 2,000 people turned out in Delhi. Protests were also being held in 15 other cities as well as in London, protest organiser Saba Dewan said.
The campaign, #NotInMyName, started with a Facebook post she wrote after a Muslim teenager was killed last week.
Many Hindus consider the cow a sacred animal.
Wednesday's protests come amid reports that a Muslim dairy farmer in Jharkhand state was assaulted and his house was set on fire after the carcass of a cow was found at his door on Tuesday afternoon.
Cow slaughter is banned in several Indian states and those found violating the law can be jailed for up to 10 years. Parliament is also considering a bill to bring in the death penalty for the crime.
But ever since the Hindu nationalist Bharatiya Janata Party came to power in the summer of 2014, vigilante cow protection groups have been emboldened and there have been numerous attacks on Muslims and Dalits, for whom beef is a staple.
Nearly a dozen people have been killed in these attacks over the past two years. Targets are often picked based on unsubstantiated rumours and Muslims have been attacked for even transporting cows for milk.
At the scene in Delhi: Geeta Pandey, BBC News
Crowds gathered at Jantar Mantar, a historical Delhi monument and popular venue for protests.
Many of the 2,000 present held posters and banners saying #NotInMyName. Others wondered if it is so easy to divide Indians on the basis of religion. On the stage, poets recited verses, and musicians sang songs of protest.
Organiser Saba Dewan demanded that Indian citizens be protected, saying the right to life is non-negotiable. One young woman told me the murders were not how she wished to remember her country.
The protest organisers have alleged that the family of Junaid Khan, the 16-year-old Muslim boy brutally killed by a Hindu mob on a train last week, had not been able to attend because they were intimidated by the authorities.
Protests under the banner #NotInMyName are being organised in 16 Indian cities, including Delhi, Mumbai, Bangalore, Chennai, Hyderabad, Lucknow and Allahabad as well as in London on Wednesday. Gatherings are also planned for later in the week in Toronto, Boston and Karachi.
The protest at Delhi's Jantar Mantar monument was expected to be the biggest, Ms Dewan said.
The documentary filmmaker said she was "shattered" when she heard about last Thursday's attack on 16-year-old Junaid Khan, who was killed by a mob of about 20 men on a train in the northern state of Haryana while returning home from Eid shopping in Delhi.
Her anguished Facebook post has managed to galvanise a large number of Indians, with thousands pledging to participate in the protests.
"The protest is against this systematic violence against Muslims and Dalits that is going on in our country at the moment," Ms Dewan said.
"Junaid's killing was a shattering moment for me, and also for a lot of other people. I started crying when I heard about his murder.
"We've always been saying we should protest, but there's been no leadership. So we decided to do this ourselves. How long can you keep waiting till the cows come home?" she added.