How do you find out how many animals live in a zoo? Grab a pencil, a clipboard and get counting!
London Zoo is home to more than 17,000 animals across over 750 species, from red-kneed spiders to Sumatran tigers, and must count them all, every year.
All British zoos must do this annually to be granted their licence.
New arrivals this year include 10 baby Humboldt penguins, three tiger cubs and six baby Philippine crocodiles - the first ever bred in Britain.
The count began today and will take about a week. Tiny creatures like ants are counted in colonies, but all others are recorded individually.
The data can be used to plan breeding programmes for endangered species.
The stock-take shouldn't be confused with the zoo's annual animal weigh-in, where all the animals get their weight checked!