The National Conference on Volunteering and Service begins in Chicago on Sunday.
It runs through Wednesday, and is billed as the world's largest gathering of volunteer and service leaders. Participants will discuss ways to spur civic engagement across the globe.
Former first lady Barbara Bush and founder of the Barbara Bush Foundation for Family Literacy will speak at the opening plenary session
Mayor Rahm Emanuel's office says the event will include service projects in neighborhoods around the city.
The event is a program of the volunteer organization Points of Light.
It will include a "youth summit" that will bring together 250 young people from around the world.
Emanuel says Chicago has a "remarkable history of combining service with innovation."