In Singapore, the Certificate of Entitlement (COE) are classes of categories as part of a quota license for owning a vehicle. The licence is obtained from a successful winning bid in an open bid uniform price auction which grants the legal right of the holder to register, own and use a vehicle in Singapore for an initial period of 10 years. When demand is high, the cost of a COE can exceed the value of the car itself. The COE system was implemented in 1990 to regulate the number of vehicles on the road and control traffic congestion, especially in a land-constrained country such as Singapore.

On 1 May 1990, the previous transportation unit of Singapore's Public Works Department (PWD) instituted a quota limit to vehicles called the COE, as rising affluence in the country catapulted land transport network usage and previous measure to curb vehicle ownership by simply increasing road taxes was ineffective in controlling vehicle population growth.

The premise was that the country had limited land resources, ie. limited supply of roads and car parks / parking lots, (with scarce land being managed to have a greater emphasis on providing an adequate supply of homes), along with demand for vehicle ownership spiralling out of control, would result in traffic conditions exceeding the criterion of a healthy road network that is sustainable by developments in land transport infrastructure resulting in gridlock.

Along with a congestion tax called the Electronic Road Pricing (ERP), the COE system is one of many key pillars in Singapore's traffic management strategies that aims to provide a sustainable urban quality of life. In place of the COE and the ERP, the government has encouraged its citizens and tourists alike to take advantage of the extensive public transportation network to get around the country instead, such as the Mass Rapid Transit (MRT), Light Rail Transit (LRT) or public buses, and to embrace a "car-lite society".

Before buying a new vehicle, potential vehicle owners in Singapore are required by the Land Transport Authority (LTA) to first place a monetary bid for a Certificate of Entitlement (COE). The number of available COEs is governed by a quota system called the Vehicle Quota System (VQS) and is announced by LTA in April of each year with a review in October for possible adjustments for the period of one year starting from May. Approximately one-twelfth of the yearly quota is auctioned off each month in a sealed-bid, uniform price auction system and successful bidders pay the lowest winning bid.

The number of COEs available to the public is regulated by the Vehicle Quota System (VQS) that is calculated every 6 months based on the following conditions:

Since the change in the total motor vehicle population is given by the number of registrations minus the number of de-registrations and any unallocated quota in a given year may be carried over to the following year, the quota formula is as follows:

In the formula above, the subscript ${\displaystyle y}$ denotes calendar year and the subscript ${\displaystyle qy}$ denotes quota year (May to April). Initially, projected de-registrations for (calendar) year ${\displaystyle y}$ were simply taken to be equal to actual de-registrations in ${\displaystyle y-1}$ but from quota year 1999–2000 onwards, a projected number of de-registrations has been used.