Stevenage manager Graham Westley will leave the club when his contract expires at the end of June.
Westley led Stevenage to six successive top six finishes having joined the Conference side when they were fighting relegation in January 2003.
"Because of the geography of the club and my expanding business interests, there is no way that I can give the club the time that it needs," he said.
"I have enjoyed my time at Stevenage where I have met some great people."
Chairman Phil Wallace paid tribute to Westley and revealed the search for new manager had started.
"Graham has made a real difference. He dragged us out of relegation danger, managed the transition to us becoming full time and almost lifted us into the Football League," he said.
"We've started listening and will see people from Monday. I doubt there'll be a shortage of people applying for the position if last time is anything to go by, but we have to balance moving quickly with making the right appointment."