PORTLAND – American folk singer, social activist and goodwill ambassador Joan Baez, whose career has spanned four decades, has become one of the foundations in the junction between traditional folk music and political activism.

On July 31, she will take the stage at Merrill Auditorium.

Baez, who immersed herself in the developing folk scene surrounding Cambridge’s fabled Club 47 in the late 1950s, has become an icon and idol for upcoming singer-songwriters and social activists alike. She has earned seven gold records and continues to raise the bar on the standards of contemporary folk music and its near first-cousins, pop, country and rock.

She remains a musical force of nature with far-reaching influence – marching on the front line of the civil rights with Martin Luther King Jr., inspiring Vaclav Havel in his fight for a Czech Republic, singing on the first Amnesty International tour, and just this year, standing alongside Nelson Mandela when the world celebrated his 90th birthday in London’s Hyde Park.

Baez’ latest album, “Day After Tomorrow,” her first new studio recording in five years, is out now. She worked with producer Steve Earle and a band that included bluegrass veterans Tim O’Brien and Darryl Scott, as well as Viktor Krauss and Kenny Malone. The album features three songs written by Earle, including “God Is God,” a song Baez debuted during her recent tour. “Day After Tomorrow” also includes songs by Eliza Gilkyson, Patty Griffin, Tom Waits, Diana Jones and Thea Gilmore.

Concert tickets are $37.50 and $42.50 (plus $2 theater restoration fee and 50 cent donation to homeless services agency Preble Street). Tickets may be purchased at the box office at 20 Myrtle St., by calling 842-0800 or online at www.porttix.com.