It’s a good time to be a countertenor. Over the last 25 years or so, 18th-century operas, most notably those by Handel, have enjoyed a rebirth in houses around the world, which has allowed the high-register countertenor male voice to sing male roles once reserved mostly for female mezzo-sopranos.

This practice will be on full display this summer in a revival of “Giulio Cesare,” which will run for 15 performances from June 23 to Aug. 23 at Glyndebourne, the summer opera festival in the rolling hills of southern England. Three countertenors have been cast, including as Julius Caesar, a vocally demanding role often given to a mezzo-soprano.

In their heyday, Handel’s operas almost always involved castrati, singers who were castrated as boys to preserve their higher voices but still gained the full lung capacity and overall stamina of grown men. (The practice largely died out in the early 19th century.) Today, however, male countertenors are being cast in roles that were once mostly written for the male voice.

Among singers, casting directors and music experts, countertenors seem to be having a moment.

At Glyndebourne, in this “Giulio Cesare” — a smorgasbord of arias, love stories, historical figures and palace intrigue that goes on for three and a half hours — the three countertenors distinguish themselves not only in character but also in voice. For Aryeh Nussbaum Cohen, who is singing the title role for the first time in a full production (he sang it in concert in Moscow in 2021) it’s a phenomenon that many opera fans might not think about for what is considered the rarest voice type.

“With each generation of countertenors, the variety seems to be so much better, and we’re in this moment of the expansion of the voice type and recognition of the variety of types of countertenors,” Cohen, 30, said in a recent video interview. “For example, nobody would think there is one type of soprano. No voice is just a monolith. But now there are coloratura countertenors. Then there are countertenors like me who have a more mezzo timbre. I have a more dramatic sound, as opposed to lyric countertenors.”

Cohen credits the casting of more countertenors over the last 25 years or so to two singers.

“The door was opened during the late ’90s by David Daniels and Andreas Scholl, who were both in their primes at the time,” he said. (Scholl famously sang in Handel’s “Rodelinda” several times at Glyndebourne and other houses to great acclaim). “The taking back of the roles by countertenors from mezzos has allowed there to be some really great singers now.”

Cohen pointed to his co-stars in the Glyndebourne production of “Giulio Cesare” as examples of the diversity among countertenors, and how voices can be matched to characters, much like the so-called Verdi tenor or Wagnerian soprano.

“Cameron Shahbazi has a more sinister quality to his voice, which suits the role of Tolomeo, the villain,” he said. “And our third countertenor, Ray Chenez, has a more light and high voice as Cleopatra’s servant, Nireno. It’s ebullient and slightly sassy and well suited to the role.”

It’s an assessment shared by those behind the casting of this “Giulio Cesare.”

“The renaissance of the countertenor voice started about 60 years ago with singers like Alfred Deller and Russell Oberlin, who were pioneers in bringing this to the public,” said Pal Christian Moe, an opera casting consultant who has worked with Glyndebourne since 2002. “It slowly caught on, but people had become accustomed to the mezzo voice in these roles.”

Other experts point out that as more countertenors have been cast in male roles, it’s created a nod to authenticity. But that isn’t an exact science.

“There is a bit of a problem in that as more countertenors have become interested in these roles, there has been a shift to treating them a bit as castrati,” Suzanne Aspden, an associate professor of music at Jesus College at Oxford University, said in a recent video interview.

“The countertenor voice is not the castrato voice. The castrati training from prepuberty was different and very rigorous. Physiologically they had greater lung capacity and were often taller.”

The idea of staging it as Handel wrote it is alluring as opera companies champion the idea of honoring the origins of his more than 40 operas.

“The presumption is that it’s a recreation of the original productions,” Aspden added. “It’s often marketed as more authentic. But we shouldn’t kid ourselves that the sound of a countertenor is going to be the same.”

But as Glyndebourne and other companies continue to embrace Handel’s operas, the more they can mix and match the mezzo-soprano and countertenor voices — or fully embrace the origins of his vision. Moe cited Glyndebourne’s production of Handel’s “Rinaldo” as a great example as it has up to four countertenor roles.

For many audiences, though, the countertenor voice is still somewhat new, or at least an anomaly.

“One director said that there are so many countertenors in the U.K. that we should try it with all countertenors, but as a group we had been thinking that it might be a bit too much for the ear,” he recalled. “But in that production, it added something to the story of Rinaldo. It worked fantastically well. We weren’t quite sure, but you don’t have a recipe for what will work. You just try it and see.”