Millions of Americans are living with autism spectrum disorder. 

According to the Center for Disease Control, autism is the fastest growing developmental disability. 

Today is World Autism Awareness Day.  

April 2 is a way to recognize autism and celebrate those who are living with it.

"Light it up blue" is a campaign celebrated on World Autism Day. 

It encourages people to wear blue and to use #LightItUpBlue to show support.

Some major landmarks will be turning blue today. In years past, the White House has lit up blue and so has Niagara Falls and the Empire State Building.