An American driving in France meets roundabouts constantly, including on rural roads where a stop sign would be the domestic answer. The preference is deliberate engineering policy.
They keep traffic moving without power
A roundabout has no signal to maintain, no power supply and no timing to adjust, which makes it cheap to run on a rural road with modest traffic.
Vehicles yield rather than stop, so a junction with light traffic imposes almost no delay at all.
That suits a country with a dense network of small roads meeting at points that could never justify a signal installation.
Collision geometry changes the outcome
A conventional crossroads allows vehicles to meet at right angles or head on, which are the collision types that produce the most severe injuries.
A roundabout converts those conflicts into merging and diverging movements at a shallow angle and at lower speed.
Crashes still happen, but the physics of the impact is different, and that difference is the main reason the design is favored.
Priority rules differ from what Americans expect
On the great majority of French roundabouts, traffic already circulating has priority and entering drivers yield, which is signed at the approach.
A small number of older roundabouts operate on the opposite principle, where entering traffic has priority, and these are signed differently.
Reading the approach signs rather than assuming a universal rule is the single most important habit for a visiting driver.
Lane use is signaled, not assumed
Multi-lane roundabouts expect drivers to choose a lane on approach according to the exit, and to signal right before leaving.
Failing to signal the exit is the most common complaint against foreign drivers, because other traffic uses that signal to decide when to enter.
Larger roundabouts on main routes have lane markings painted through the circle, and following the painted line matters more than judging by eye.
What else the visiting driver should expect
Roundabout centers are frequently used for public art and planting, which obscures the view across and makes it harder to judge approaching traffic early.
Rural roundabouts often appear immediately after a speed reduction, and the approach speed is the thing most likely to catch out a driver used to open highway limits.
Trucks take a wide line through larger roundabouts and may occupy more than one lane, so leaving space rather than overtaking inside is the safer choice. Their path through the circle is dictated by the trailer, not the cab.
Roundabouts also appear on the approach to motorway junctions, which means a driver may pass through several in quick succession while looking for an exit that is signed only once.