A monopoly (lower case "m") is when a player owns all of the properties of one color. When a monopoly is owned, the owning player can build houses or hotels on it and, if unimproved, receive double rent from it. Houses and Hotels are used to improve the rent of a property. Houses and hotels can only be erected if a complete monopoly is owned.
List of Monopolies (UK)
- Brown: Whitechapel Road and Old Kent Road
- Light Blue: The Angel Islington, Euston Road and Pentonville Road
- Pink (aka Light Purple): Pall Mall, Whitehall and Northumberland Avenue
- Orange: Bow Street, Marlborough Street and Vine Street
- Red: The Strand, Fleet Street and Trafalgar Square
- Yellow: Leicester Square, Coventry Street and Piccadilly
- Green: Regent Street, Oxford Street and Bond Street
- Dark Blue: Park Lane and Mayfair
List of Monopolies (US)
- Brown (or Dark Purple): Mediterranean Avenue and Baltic Avenue
- Light Blue: Oriental Avenue, Vermont Avenue and Connecticut Avenue
- Pink (aka Light Purple): St. Charles Place, States Avenue and Virginia Avenue
- Orange: St. James Place, Tennessee Avenue, New York Avenue
- Red: Kentucky Avenue, Indiana Avenue, Kentucky Avenue
- Yellow: Atlantic Avenue, Ventnor Avenue, Marvin Gardens
- Green: Pacific Avenue, North Carolina Avenue, Pennsylvania Avenue
- Dark Blue: Park Place, Boardwalk
Train Stations (King's Cross Station / Reading Railroad, Marylebone Station / Pennsylvania Railroad, Fenchurch St Station / B. & O. Railroad and Liverpool Street Station / Short Line) and Utilities (Electric Company and Water Works) are not color group monopolies as defined herein and Houses/Hotels cannot be erected on them. However, they are like monopolies in that you can collect more than one of each and rent is higher when more than the first rent.
Train Depots could be built on Railroads in the Mega Edition for $100, but not in the standard US or UK versions.