Glasgow Kelvin College and New College Lanarkshire, as well as North East Scotland College and Dundee and Angus College, all come into being.
The new higher education hubs are designed to support students into work.
Cabinet Secretary for Education Michael Russell praised the four mergers.
He said: "The aim of these reforms has always been about making the college sector work for students, communities, staff and employers.
"By creating colleges of scale and influence, and combining resources and expertise, we make the journey onto further learning or into work easier."
Glasgow Kelvin College brings together North Glasgow, Stow and John Wheatley colleges. It will host an official opening on November 4.
Motherwell and Cumbernauld colleges will become New College Lanarkshire. The board has agreed Coatbridge College will unite with them in 2014.