Former All-Ireland champion Brenda Castles, outstanding on both concertina and tin whistle, and The Fretless, a Canadian quartet that has championed the “chambergrass” folk-string ensemble sound, will make their debuts at this year’s “A Christmas Celtic Sojourn,” along with an up-and-coming Scottish singer with the singular name of Hannah Rarity.

The annual holiday show, featuring music, song, dance, and storytelling from Irish, Scottish, and other Celtic – even non-Celtic – traditions, makes its customary stop at the Cutler Majestic Theatre at Emerson College in Boston from Dec. 14 to Dec, 16, with additional performances at Rockport’s Shalin Liu Performance Center (Dec. 12), Worcester’s Hanover Theatre (Dec. 18), the Zeiterion Theatre in New Bedford (Dec. 19) and Providence’s Veterans Memorial Auditorium (Dec. 20) before returning to the Cutler to close out its run Dec. 21-23.

Returning for a second time to “Sojourn” will be four-part harmony a cappella group Windborne and guitar-bouzouki-harmonium player Owen Marshall, joined by musical mainstays cellist Natalie Haas; bassist Chico Huff; percussionist Ben Wittman; and the show’s assistant and chief musical directors, respectively, harpist Maeve Gilchrist and multi-instrumentalist Seamus Egan.

National Endowment for the Arts award winner Kevin Doyle, another veteran of the show, will again serve as dance director. Joe Duffey, an acclaimed Irish dance performer, choreographer, and instructor from Washington, DC, and the ever-popular Harney Academy of Irish Dance from Walpole also will be part of the festivities.

As always, hosting the production is “Christmas Celtic Sojourn” creator Brian O’Donovan of WGBH-FM’s “A Celtic Sojourn,” which serves as a template for the show. O’Donovan and his wife Lindsay will provide additional vocals for “Sojourn,” as will Gilchrist and Castles.

“It’s amazing to think that in a few weeks, we’ll be starting up the rehearsals,” said O’Donovan, interviewed shortly before Thanksgiving. “Of course, we do all kinds of work and preparation before that, by Skype or phone or e-mail or whatever. But then we’ll gather for several days, just hunker down and put everything together. It’s very intensive, but loads of fun, and quite satisfying.”

County Meath native Castles – who appeared in this year’s “St. Patrick’s Day Celtic Sojourn” – grew up in a musical family, and earned All-Ireland Fleadh titles in solo and group competitions. She learned tin whistle and concertina from Rena Crotty Traynor, and later with Mícheál Ó’Raghallaigh, one of the most respected concertina players today. She has recorded a solo album, “Indeedin You Needn’t Bother,” which includes her own compositions as well as tunes from distinguished musician/composers like Ed Reavy, Vincent Broderick, and Charlie Lennon.

“There’s actually quite an impressive legacy of female concertina players in Ireland,” says O’Donovan. “When the instrument first came along in the 19th century, apparently it was seen as perfect for women: a good size for their ‘delicate’ hands, and nothing flamboyant. Well, Brenda is part of a long line of women like Mary MacNamara and Edel Fox –  just to name a few – who have become phenomenal concertina players.”

The Fretless (fiddle and viola players Trent Freeman, Karrnnel Sawitsky, and Ben Plotnick, and cellist Eric Wright) explores the rhythmic, harmonic, and structured arrangement of Celtic, old-timey, bluegrass and other folk/traditional styles in the essence of a chamber string quartet, hence the descriptive phrase “chambergrass.” The band, and chambergrass itself, has a Boston connection: Freeman and Wright were Berklee College of Music students, and founded The Fretless with fellow Berklee acquaintance Ivonne Hernandez, who was active in the Boston music scene. The band’s most recent album, “Live at the Art Farm” – which focuses on the traditional Irish part of its repertoire – has earned them well-deserved attention, says O’Donovan.

“They’ve really come into their own, and developed an amazing sound. We’re particularly excited to have them in the show this year, not only for what they bring as a quartet but also because it sets up some intriguing possibilities, such as a two-cello dynamic with Natalie, or a strings-and-harp thing with Maeve.

“So, put them all together with Seamus and the all instruments he plays, plus our terrific rhythm section of Ben, Chico and Owen, and the music will be as strong as ever.”

Rarity (actually pronounced “RAW-itee”), the BBC 2018 Young Scottish Traditional Musician of the Year, recently released her first full-length album, “Neath the Gloaming Star,” showcasing her command of both traditional and contemporary material and styles. Having toured the US previously with Cherish the Ladies, Rarity will make her American solo debut with “Christmas Celtic Sojourn.” She joins an impressive roster of female singers – among them Karan Casey, Cara Dillon, Karine Polwart, Alyth McCormack, and Mairi Campbell – who have been part of the show over the years.

“We’ve certainly featured male singers, like Sean Keane and Robbie O’Connell, but having a female voice just really seems to suit the spirit of the season, and of the event,” says O’Donovan. “There’s something of the divine feminine, the quality of ‘a mother’s love,’ to Christmas, and so it’s natural to have the show reflect this. Hannah is a great personality as well as a talented singer, and we’re happy to welcome her this year.”

O’Donovan also is pleased to have Windborne (Jeremy Carter-Gordon, Lynn Mahoney Rowan, Will Thomas Rowan, and Lauren Breunig) back, for reasons that go beyond their exhilarating brand of singing and imaginative repertoire.

“These are young people who grew up in the Boston and New England folk scene, and were involved in things like Revels, Village Harmony, and other events and activities,” he explains. “They have a good feel for ritual and ceremony, and are outstanding collaborators. And I should mention that they are incredible actors, too, which is a good talent for the show: In recent years, we’ve been incorporating some vaudevillian, tongue-in-cheek stuff, like ‘Miss Fogarty’s Christmas Cake,’ and they totally get into it.”

Doyle, a sprightly presence for many years in “Christmas Celtic Sojourn,” is concentrating more on the choreographic and artistic elements of the show’s dance content – although “it may be difficult to keep him completely in the background,” O’Donovan deadpans. As this year’s featured dancer, Duffey brings two decades of experience in Irish dance, nurtured in the lively Washington, DC-area Irish community. In addition to traditional dance activities and performances, he has toured with “Riverdance” and worked directly with Michael Flatley in “Lord of the Dance.”

The Harney Academy of Irish Dance has assumed a multi-generational role in the show, with the current school-age students supplemented by appearances from some Harney alumni.

“It’s been wonderful to see the little kids grow and mature, and come back as young adults to bring their own kind of energy,” says O’Donovan. “And, of course, there’s a whole new generation of Harney dancers who are learning the ropes, and keeping the cycle going. That’s how traditions thrive.”

For ticket information and other details about this year’s “A Christmas Celtic Sojourn,” go to wgbh.org/celtic.