Safe-standing areas will be allowed on a trial basis at European club games involving teams from England, Germany and France this season, UEFA said on Wednesday.
European football's governing body said it would assess the findings of what it calls an "observer programme" at the end of the season and decide whether to continue or expand the trial.
The three countries in question are already authorised to have safe standing at domestic level. In England, Manchester City, Manchester United, Liverpool, Chelsea and Tottenham Hotspur all have safe-standing licenses.
Borussia Dortmund, whose stadium has a vast standing area called the "Yellow Wall," said they would be able to host Champions League games at their full 81,365 capacity for the first time.
The German club use safe-standing areas for domestic games but have had to convert those sectors into seating for European games. That reduces the stadium's capacity by about 15,000.
"That's great news. Standing tickets are an important part of our football culture. Borussia Dortmund have been working hard behind the scenes in recent years to obtain permission for safe-standing areas in European competitions," CEO Hans-Joachim Watzke said. He called on fans to "behave responsibly with this opportunity."
UEFA is limiting the trial to the top five associations in its rankings. Spain and Italy do not have safe-standing areas.
The final of each of the three UEFA competitions will be excluded from the trial.
"The objective," UEFA said, "is to assess if and under what conditions standing may be reintroduced in UEFA competitions in a safe manner."