Crown Prince Mohammed bin Salman's three-day visit to the UK is expected to be dominated by protests.
Here we look at why:
What is Saudi Arabia's role in the war in Yemen?
Yemen has been embroiled in a bloody civil war since 2014 when Houthi rebels took over the capital city of Sanaa. Saudi Arabia feared the rise of the group it says is backed by Iran, the region's key Shia power. Riyadh formed a coalition with other mainly Sunni Arab states to restore the ousted Yemeni government.
What action has Saudi Arabia taken?
As well as bombing campaigns, the kingdom hit Yemen with naval blockades after a missile was fired towards Riyadh. The ports of Hodeidah and Salif were blocked off for weeks, stopping crucial aid and supplies from reaching the country.
How has the conflict affected Yemenis?
The UNHCR, the United Nations' refugee agency, says the country is suffering the "world's worst humanitarian crisis". Some 22.2 million people, 75% of the population, are in need of aid as they battle conflict, famine and disease, and thousands have died.
Does the Saudi coalition have international support?
The UK is not part of the coalition but Saudi Arabia is its key ally in the region. Campaigners lost a legal bid to stop Britain selling arms to the kingdom while it continues its military campaign against the Houthis. The US has provided intelligence and other support for the coalition.
Is the crown prince's visit controversial for other reasons as well?
Yes. Although the crown prince has very publicly embarked on a modernisation programme in the kingdom, critics say it is little more than a smokescreen. Rules banning women from driving are being lifted but they still need permission from a man to travel, get a job or receive an education. Human rights charity Reprieve claims executions have doubled under the crown prince.