Three new theaters are slated to open in different parts of Boston by the end of 2021, with a collective capacity of nearly 11,000. Each will be attached to a major existing site, including Fenway Park and TD Garden. Here are the details.

Big Night Live

A pair of major concert operators is planning to open a 2,000-person performance venue in the fall of 2019 next to TD Garden.

The 40,000-square-foot venue—which would seat 1,500 for a live performance—would be called “Big Night Live” and would be part of the ginormous Hub on Causeway project that is unfolding in the same area (and TD Garden itself is undergoing quite a bit of big change too).

The venue’s backers, Big Night Entertainment and Live Nation, tell the Globe’s Tim Logan that a 200-seat Mexican restaurant will be part of the club, which will have multiple tiers and big windows behind the stage that look out at Boston Harbor and the Zakim Bridge.

Boston Landing

Concert promoter the Bowery Presents is planning a 3,500-capacity, general-admission performance venue at the massive Boston Landing complex in Brighton that already includes practice facilities for the Celtics and the Bruins.

The venue is set to anchor a portion of the mixed-use complex at Boston’s western edge called “The Track at new balance”—sneaker concern New Balance is behind Boston Landing—according to a release from the Bowery Presents.

Construction is scheduled to start in April, with an opening anticipated in fall 2021. The venue’s name and other details are to be decided, the release said. (There are no renderings yet either.) The Bowery Presents’ stable already includes Boston’s Royale and the Sinclair in Cambridge.

The Fenway Theater

Construction on a new theater next to Fenway Park could commence as soon as after the upcoming baseball season and wrap in the summer or fall of 2021, according to plans filed recently with the Boston Planning & Development Agency by an affiliate of the ownership group of the Red Sox and Fenway Park.

We’ve known since late September that the group had a big plan for a triangle of land where Ipswich and Lansdowne streets meet just beyond the famed ballpark. The filing provides the most details yet on it.

The theater would be a “state-of-the-art, multipurpose” performance venue with capacity for as many as 5,400, according to the filing.

It “is intended to fill a void in the landscape of performing arts venues in the greater Boston area by providing a facility whose capacity sits between venues that accommodate less than 2,500 patrons and the larger arena/stadium venues.”

The venue will host events year-round. And, to make room for it, the ownership group plans to relocate current service, loading, and receiving activities from the triangular space to newly constructed, off-street, interior loading dock bays within the Fenway Garage.

What’s more, mail and ground-slash-concessions facilities that also occupy the site will be relocated to within the ballpark or moved elsewhere.

The theater is still in what its backers call “the early design stages.” But, pending the necessary approvals, that construction could start once the Red Sox season wraps this year. The backers are hoping to complete most of the construction before the new Boston Arts Academy opens across Ipswich street. That is also scheduled for 2021. Stay tuned.