Police said a man was shot in a paramilitary-style attack "by appointment".
It happened in the Hazelwood Avenue area of west Belfast on Tuesday night.
Detective Sergeant Eric Fairfield said: “We received a report at around 10.30pm from the Northern Ireland Ambulance Service, that a man had been shot in the leg.
“The victim, who is in his 30s, was taken to hospital for treatment of injuries to his leg.
"We believe at this time that the shooting was by appointment and that the man had been ordered to attend this location to be shot.
"This is totally barbaric and must stop. No-one deserves to have this happen to them and there is absolutely no justification for an attack like this in our communities.
"We must all work together to bring those responsible to justice and to stop this from happening to anyone else."
The officer added: "Our enquiries are at an early stage, however, we are treating this as a paramilitary-style attack and I want to appeal to anyone who has information which may assist our investigation to pick up the phone and tell us what you know.
“If you have any information which may assist with our enquiries, please contact detectives on 101 quoting reference number 2181 of 16/06/20. Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”