Host city Vienna has been bedecked in hearts and the contest's "United by Music" motto for a week in which singers and bands from 35 countries will compete onstage for the continent's musical crown.
But five countries - Spain, Ireland, the Netherlands, Slovenia and Iceland - are boycotting to protest Israel's inclusion.
Several pro-Palestinian demonstrations are planned in Vienna during Eurovision week, and security is tight, with police officers from across Austria deployed in the capital, and support from forces in neighbouring Germany.
Israeli singer Noam Bettan is among 15 acts competing for votes from viewers and national juries in Tuesday's semi-final at the Wiener Stadthalle arena.
The top 10 will go through to Saturday's grand final, along with 10 from Thursday's second semi-final.
The UK, France, Germany and Italy automatically qualify because they are among the contest's biggest funders.
Austria, the 2025 winner, goes through to the final as host country.
Bettan is seeking to get Israel, which came second in 2025, into Saturday's final with the ballad Michelle.
Like 2025's Israeli competitor, Yuval Raphael, he has practised singing while being booed.
Hoping to cement its status as bookmakers' favourite is Finland, with the intense Liekinheitin (Flamethrower) by violinist Linda Lampenius and pop singer Pete Parkkonen.
Other competitors in Tuesday's semi-final include Greece's Akylas with fan-favourite party-rap track Ferto (Bring It); Portuguese quintet Bandidos do Cante with the soulful Rosa; and singer Senhit, representing tiny San Marino with Superstar, a party anthem featuring a guest appearance by Boy George.
Delta Goodrem is representing Australia with her song Eclipse in the second semi-final.
Long a forum for good-natured national rivalries, Eurovision has found it hard to separate pop and politics in recent years.
Russia was expelled in 2022 after its full-scale invasion of Ukraine.
The 2024 contest in Malmo, Sweden, and 2025's event in Basel, Switzerland, saw pro-Palestinian protests that called for Israel to be expelled over its conduct of its war against Hamas in Gaza and allegations it ran a rule-breaking marketing campaign to get votes for its contestant.
When organisers declined to kick Israel out, five countries announced in December they would not take part in 2026.
Dean Vuletic, author of Postwar Europe and the Eurovision Song Contest, is confident Eurovision can weather the latest storms.
"We'll see demonstrations, but we'll also see a lot of colourful events going on which will really represent what Eurovision is about, which is bringing Europeans together," he said.
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