The mission of remaking cities to become more sustainable, productive, liveable, resilient, and inclusive is a twenty-first-century grand challenge. This chapter reports on the application of urban transition frameworks and processes in the development and implementation of a new planning model for regenerating and re-urbanising Australia’s low-density, car-dependent greyfield suburbs: the established, ageing, but well-located middle-ring suburbs built in the post-war era on larger lots. Most housing in these areas has now reached the end of its service life and is prime for redevelopment. Since greyfields comprise most residentially zoned land in cities, this positions them as the critical entry points for regenerative, medium-density, compact city redevelopment. But the wrong planning models are being used. Most infill redevelopment in greyfields is fragmented, piecemeal, small-lot subdivision, delivering a low yield of new housing, significant loss of greenspace, and no added services, infrastructure, or residential amenity. This chapter introduces greyfield precinct regeneration (GPR), the product of a set of innovative, transition-oriented planning concepts, models, tools, and processes capable of regenerating established, ageing precincts in occupied greyfields: a mission-scale challenge. It provides a blueprint for mainstreaming GPR, illustrated with a case study from a middle-suburban municipality in Melbourne that charts the urban transition from concept to implementation.