Three masked men carried out an attack in Berkhamsted High Street that left the victim with a stab wound to the abdomen.
The men, who were in balaclavas, got out of a Mercedes to carry out the attack just before midnight on Saturday.
Hertfordshire police, who closed the High Street on Sunday for investigation work, are hunting the men.
They said: “Police were called at 11.57pm on Saturday (June 13) to reports of an assault in Berkhamsted High Street. Officers attended the scene and found a man who had sustained an alleged stab wound to his abdomen.
“He was taking to hospital and remains in a stable condition. His injuries are not thought to be life-threatening. The offenders, described as three males wearing balaclavas, are believed to have exited a vehicle, possibly a white Mercedes, before assaulting the victim. Officers searched the area but they remain outstanding at this time.”
Detective Inspector Nick Rega said: “I understand this news will be alarming to residents and I want to reassure you that we are doing all we can to trace those responsible. If you saw what happened or have any information about the incident, please call the non-emergency number 101 quoting crime reference 41/46207/20. You can also report information online at herts.police.uk/report or speak to an operator in our Force Communications Room via our online web chat at herts.police.uk/contact.
Alternatively, you can stay 100 per cent anonymous by contacting the independent charity Crimestoppers on 0800 555 111 or via their untraceable online form at crimestoppers-uk.org.