By Clarence Fanto, Special to The Eagle

LENOX — At some point during his Tanglewood shows on Monday and Tuesday night, James Taylor will bring on a surprise guest to share the spotlight before a capacity crowd of about 18,000 ardent fans.

Singer-songwriter Bonnie Raitt, an old friend of Taylor’s since they first performed together in Cambridge in 1970 when she was a Harvard junior and a newly minted blues singer, is a natural for a joint appearance, since they are about to launch a six-week national tour of 17 cities, including several baseball stadiums. They’ll be returning to Fenway Park for Taylor’s third annual appearance there — Raitt joined him in 2015.

At Tanglewood, “we’ll do a tune or two of hers, a tune or two of mine, it’s a simple guest spot,” said Taylor in a wide-ranging interview this week.

A limited number of tickets were available for the 8 p.m. shows on Monday and Tuesday, as of Saturday morning. The Independence Day performance, with proceeds donated back to Tanglewood by James and Kim Taylor, is followed by the annual fireworks show over Stockbridge Bowl.

Recalling her first gig with Taylor 47 years ago, Raitt said in an Associated Press interview, “I was nervous to play because I hadn’t really broken my chops in for concerts that much. But I was so excited. It was an honor to be both at my school and opening for him. He couldn’t have been warmer and more friendly. It was intimidating to meet one of my heroes, but he was just so down to earth.”

About to make his 25th set of appearances at the Boston Symphony’s summer home since his debut there in 1974 with Linda Ronstadt as the opening act, Taylor emphasized that “Tanglewood has been this incredible part of my professional life.”

Since the turn of the century, he has returned annually, with rare exceptions, and he credits his wife, Kim — a former BSO executive and current trustee — “for opening my eyes to Tanglewood and bringing me back here. It’s a great connection, one of the best things that’s ever happened to me.”

With keen anticipation, he discussed the upcoming tour, which begins Thursday at the Prudential Center in Newark, N.J.

“I’ve been aware of Bonnie and her music since she started,” he said. “She was an early musical friend since we performed together on Martha’s Vineyard in those great days when it was a destination for artists and intellectuals who wanted a cheap vacation. I’ve been eager to play with her some more since that first show at Fenway.”

This week, Taylor and Raitt have been rehearsing at the 17,000-seat Times Union Center in Albany, N.Y., which can accommodate the elaborate staging needed for the large arenas and stadiums where they’ll be performing, including Nationals Park in Washington, D.C., Wrigley Field in Chicago and AT&T Park in San Francisco. The tour ends at Fenway on Aug. 11.

Tanglewood audiences will get a sample of their vocal collaboration because, as Taylor pointed out, “it doesn’t have room for the staging we’ll be taking around the country, since it’s primarily an acoustic musical house.”