Local government across England is often referred to as a patchwork.
Some places have both district and county councils that each provide some services; some places have one council that does everything, and some places have a mayor who oversees that.
Rayner's plan is to make the system similar across England. So bins and libraries, planning and leisure centres will all fall under one, single council.
The government says merging councils could save £2bn. That comes amid a bleak picture of council finances across the country.
Neighbouring areas would then be grouped together under what's called a strategic authority with a directly elected metro mayor. Recent examples of this include Nottinghamshire and Derbyshire, who now fall under the East Midlands Combined County Authority, and elected their first mayor, Labour's Claire Ward, in May.
Half of the population of England currently have an elected mayor, with research suggesting they're well known locally.
Polling from the non-partisan think tank the Centre for Cities suggests that mayors are the most recognisable local political figures in their area, with three-quarters of people knowing who they are - way ahead of MPs or council leaders.