Many left their normal school uniforms at home and instead dressed up for the day as characters from their favourite books.
World Book Day was created by UNESCO in 1995 and now is marked in more than 100 countries. The first World Book Day in the UK and Ireland took place in 1997 to encourage young people to discover the pleasure of reading.
We asked schools to send in photos taken on the day – and here they are!
1. Carleton Park Junior & Infants School
There were some fabulous costumes and characters arriving at Carleton Park. Photo: submit
2. St John the Baptist Catholic Primary School
Year 1 celebrating World Book Day at St John the Baptist Catholic Primary School. Photo: submit
3. St Ignatius Catholic Primary School
Happy chidlren in the Early Years Foundation class at St Ignatius Catholic Primary School. Photo: submit
4. St Ignatius Catholic Primary School
St Ignatius Catholic Primary School Class 1. Photo: submit