The brief proposes a radical £140m transformation of Union Terrace Gardens, including covering over an unattractive dual carriageway and railway line.
Designers will improve street level access and create "sparkling green public spaces and new routes," said competition organiser Malcolm Reading Consultants.
"The team will connect areas that have become detached and provide a place for outdoor events. This is a rare opportunity to redesign the centre of this eminent city," the invitation added.
The 6ha site suffered from awkward changes of level, poor access and under use despite its potential as a green public and cultural space, said the firm.
"It is adjacent to the historic spine of Union Street and at the nub of the city. Gardens and landscaping will define a civic space for outdoor events, a new cultural centre, a cafe quarter and links with bus and railway stations."
Competition deadline is 13 June and each team should include an urban designer, architect and structural and civil engineers as well as a landscape architect. "For any designer passionate about cities and how to make them inspiring and alive, this is a chance to make their name and reputation," said the organiser.
Malcolm Reading has run competitions for the Victoria & Albert Museum, the British Pavilion for Shanghai World Expo 2010 and Glasgow School of Art.