The Duke and Duchess of Cambridge have arrived in New York for a tour of the east coast of the United States.
The couple are in the country for three days, during which Prince William will meet President Barack Obama.
Catherine, who is pregnant with the couple's second child, will accompany the duke to pay respects to those who died in the 9/11 terror attacks.
Danny Lopez, the British consul general in New York, said there had been "incredible interest" in the visit.
He added there has been a huge "level of excitement" from people in the city.
Prince William is also expected to give a speech at a World Bank conference in Washington on combating illegal wildlife trafficking.
Highlighting the scale of the problem the prince is expected to say "some endangered species are now literally worth more than their weight in gold".
By BBC royal correspondent Nicholas Witchell
Compared to their other big foreign trip this year, to New Zealand and Australia for three weeks in April, this one is a blink-and-you'll-miss-it experience.
Except that this is New York and Washington, so the scrutiny will be intense and the long-term impressions will matter.
The Americans have an ambivalent attitude to royalty. To some it represents a social structure which they find offensive, where birth counts for more than worth, but they do seem to find it intriguing, and in William and Catherine they perceive a couple who fulfil several of the critical American benchmarks of success.
They are glamorous and they have a status which appears to transcend the shallowness of mere "celebrity".
For the two days she is in New York, Catherine's appearance, her clothes and the state of her pregnancy will be endlessly examined and analysed.
For William especially, these two days in the United States will be a chance for him to define more clearly how he will approach his future role.
The prince is set to describe the trade in elephants tusks, rhino horns and other animal parts as "one of the most insidious forms of corruption and criminality in the world today".
His speech is also expected to make reference to China, which has a market for endangered animal parts, and say that the wholesale price of ivory has risen from $5 (£3) to $2,100 (£1,348) per kilogramme in the last 25 years.
The duke will argue that this price hike has increased poaching around the world, and he will urge people to take action.
'Mankind's ignorant craving'
He will say: "Our collective goal must be to reduce the wildlife trade by making it harder: denying traffickers access to transportation, putting up barriers to their illegal activities, and holding people accountable for their actions.
"Those who look the other way, or spend the illicit proceeds of these crimes, must be held to account."
And talking about those who engage in the trafficking of animal parts he will say: "Together they loot our planet, to feed mankind's ignorant craving for pets, trinkets, cures and ornaments derived from the world's vanishing and irreplaceable species."
William will be joined by former foreign secretary William Hague, who hosted the government's conference on illegal wildlife trade in February.
President Obama has welcomed the prince's work on the issue, which he called "a devastating environmental problem".
Elsewhere, the couple are set to attend an NBA basketball match during the trip.
The duchess will also visit an organisation supporting families in Harlem called the Northside Centre for Child Development.