Performers from 15 countries battled it out in front of thousands of fans in Basel, Switzerland for 10 spots in Saturday's final, with the result decided by viewers' votes.
Betting market favourites KAJ, a trio of Swedish-speaking Finns, performed Bara Bada Bastu, a catchy ode to steam and heat whose title translates roughly as "just take a sauna", accompanied by dancers dressed as lumberjacks and clad in towels.
Joining KAJ in the final is another favourite with oddsmakers, 21-year-old Dutch singer Claude with soulful, Parisian-style ballad C'est La Vie. Claude hopes to win for his country after the Netherlands' 2024 contestant, Joost Klein, was kicked out of Eurovision over a backstage altercation.
Others voted into the final include Icelandic brother duo VAEB with a rap song about rowing, Róa, Norwegian singer Kyle Alessandro's Lighter and two uber-Italian songs that aren't from Italy: DJ Gabry Ponte, representing San Marino with the upbeat Tutta L'Italia and the highly caffeinated Espresso Macchiato by Estonia's Tommy Cash.
Ukraine, Portugal, Poland and Albania also made the final. Azerbaijan, Belgium, Croatia, Cyprus and Slovenia were eliminated.
Music fans across Europe and beyond have travelled to the northern Swiss city of Basel, which is hosting Eurovision because Swiss singer Nemo won last year's contest in Sweden.
Canadian chanteuse Celine Dion, who won Eurovision for Switzerland before she became a mega-star, sent a video message that was played before some of last year's competitors performed her 1988 contest-winning song, Ne partez pas sans moi.
Viewers were also entertained with a comic song performed by hosts Hazel Brugger and Sandra Studer celebrating Swiss inventions including the Swiss Army knife, muesli, processed cheese - and Eurovision, first staged in Lausanne in 1956.
Tuesday's showdown and a second semi-final on Thursday will narrow the field of 37 nations down to 26 who will compete in Saturday's grand final. Twenty finalists will be decided by viewers' votes, while six countries automatically qualify for the final: the host, Switzerland, and the "Big Five" who pay the most to the contest - France, Germany, Italy, Spain and the UK.
Flying the flag for Australia is singer-songwriter Marty Zambotto, better known by his stage name Go-Jo, who will perform Milkshake Man in Thursday's semi-final (on Friday, Australian time).
Eurovision was founded partly to foster unity on a continent scarred by World War II, and its motto is United by Music. But political divisions often cloud the contest, despite organisers' efforts to keep politics out.
Officials say more than 1000 police officers are on duty in Basel this week, and organisers are expecting protests against Israel's participation because of the country's conduct of its war against Hamas in Gaza.
A demonstration against anti-Semitism is also planned on Thursday, the day Israeli singer Yuval Raphael performs in the second semi-final.
Raphael is a survivor of Hamas militants' October 7, 2023, attack on southern Israel that killed 1200 people. More than 52,800 people in Gaza have been killed in Israel's retaliatory offensive, according to the territory's health ministry.
Following tensions over Israel's participation and Klein's expulsion in 2024, the European Broadcasting Union that organises Eurovision has tightened the contest's code of conduct, calling on participants to respect Eurovision's values of "universality, diversity, equality and inclusivity" and its political neutrality.
Audience members will be allowed to wave Palestinian flags inside Basel's St Jakobshalle arena, after a contentious ban last year. Participants, however, can only wave their own national flag onstage or in other on-camera areas. Some delegations have protested that effectively bans LGBTQI pride flags from an event with a huge gay following.
