Unlike traditional automatic transmissions, CVT (continuously variable transmissions) don't have a gearbox with a set number of gears, meaning they don't have interlocking toothed wheels.  The most common type of CVT operates on a pulley system that allows an infinite variability between highest and lowest gears with no discrete steps or shifts.  

CVT's offer constant acceleration from a complete stop to cruising speed.  This eliminates "shift shock" and makes for a smoother ride.  The transmission works to keep the car in its optimum power range regardless of how fast the car is traveling.  CVT's offer improved fuel efficiency.  They respond better to changing conditions, such as changes in throttle and speed.  There is less power loss in a CVT than in in a typical automatic transmission and better control over emissions.