President Trump has made the release of the remaining Israeli hostages held by Hamas a central part of his push for a cease-fire in the Gaza Strip.

In the assault on Israel two years ago that started the war, Hamas and other militants took about 250 people captive and brought them back to Gaza, though in a few cases the hostages had already been killed and their bodies were taken back.

Here is what to know about those who remain:

How many hostages are in Gaza?

Israel says that there are still about 20 living hostages in Gaza, along with the bodies of around 25 others.

Mr. Trump’s cease-fire proposal last month called for the release of all hostages, both living and dead, within 72 hours of Israel accepting the plan. But Israel agreed nine days ago, so the timing now is unclear.

Videos released by Hamas have shown captives looking emaciated and frail, shocking many Israelis and raising questions about how much longer they can survive.

Hamas officials said last month that returning the bodies of dead captives would mean retrieving them from where they were buried, which would take time.

What happened to the other hostages?

Many of the people kidnapped on Oct. 7 have been freed in exchange for Palestinian prisoners held in Israeli jails during two cease-fires, one in the early months of the war and a second earlier this year. At least eight other hostages were freed in Israeli military operations.

More than three dozen hostages have been killed in captivity, according to an investigation by The New York Times.

Seven hostages were executed by their captors as Israeli soldiers drew near, and four others died in Israeli airstrikes, according to Israeli officials and the public findings of military investigations.

Three hostages were killed by Israeli soldiers who mistook them for Palestinian militants, the Israeli military has said; one was shot and killed in a crossfire. The circumstances surrounding the deaths of the others remain unclear.

What does Hamas get in return?

Under the Trump plan, once the hostages are freed, Israel would “release 250 life sentence prisoners plus 1,700 Gazans who were detained after Oct. 7, 2023.”

“For every Israeli hostage whose remains are released, Israel will release the remains of 15 deceased Gazans,” the plan says.

The timing of the Israeli prisoner releases is unclear.