From New York to Sydney, Antrim to Londonderry – towns and cities around the world have joined forces to raise awareness of autism.
The Empire State Building and Sydney Opera House are two of the most famous buildings in the world, and now Antrim Civic Centre and Derry City Council offices have appeared in lights alongside them.
A total of 23 councils around Northern Ireland lit up their civic buildings in blue at the same time as landmarks such as the Pyramids in Egypt and Nelson's Column.
Queen's University in Belfast and the Great Hall at Stormont were also turned blue as part of global efforts to mark Autism Awareness Month.
There are currently more than 20,000 people with autism in Northern Ireland – more than the total number of those affected by Down's syndrome, multiple sclerosis and Parkinson's disease.
Autism NI's chief executive Arlene Cassidy said: "It is vital that awareness is raised throughout Northern Ireland for autism. By holding an event such as this, the Northern Ireland Assembly has helped to highlight this hidden disability."
To sign up for a 5km walk at Stormont for Autism NI, contact Rachel Gribben on 028 9040 1729 or email firstname.lastname@example.org.