Sport's highest court has rejected appeals by 45 Russian athletes and two coaches who were banned from the Pyeongchang Olympics - less than nine hours before the opening ceremony.
The Russians had appealed their exclusion from the Winter Olympics by the International Olympic Committee (IOC) over the 2014 Sochi Games doping scandal.
The Court of Arbitration for Sport ruled that the IOC has the right to set its own standards for who is eligible.
CAS secretary general Matthieu Reeb said the IOC process "could not be described as a sanction but rather as an eligibility decision".
"There was no finding that this was carried out in a discriminatory, arbitrary or unfair manner," he added.
In a statement, the IOC said: "We welcome this decision which supports the fight against doping and brings clarity for all athletes."
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A vetting process was designed to exclude Russian athletes from the Games if IOC officials weren't sure they were clean, even if they hadn't been banned for doping.
The IOC has invited 168 Russians to participate as "Olympic Athletes from Russia", competing in neutral uniforms under the Olympic flag.
The ruling comes a day after the first Olympic competitions began and ends more than a week of uncertainty for two groups of athletes who lodged appeals to the CAS.
In December, the IOC banned Russia from the Games over manipulation of doping samples at the Sochi Olympics.
It also banned dozens of athletes from the Games for life and stripped their Sochi Games medals following several investigations into the doping affair.
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A high-level North Korean government delegation - including Kim Yong Nam, the country's nominal head of state, and Kim Jong Un's younger sister, Kim Yo Jong - has arrived in South Korea to attend the Games' opening ceremony.
Kim Yo Jong is the first member of North Korea's ruling family to visit the South.
The delegation will have lunch with South Korean President Moon Jae-in on Saturday.
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US Vice President Mike Pence arrived in South Korea on Thursday and had talks and dinner with President Moon.
Both men reiterated their commitment and co-operation to defuse tensions on the Korean peninsula sparked by North Korea's missile and nuclear programmes.
Mr Pence has met North Korean defectors and is expected to pay tribute to a memorial for 46 South Korean sailors killed in 2010 in the sinking of a warship that Seoul blamed on a North Korean torpedo attack.