The RATP bus network covers the entire territory of the city of Paris and the vast majority of its near suburbs. Operated by the Régie Autonome des Transports Parisiens (RATP), this constitutes a dense bus network complementary to other public transport networks, all organized and financed by Île-de-France Mobilités.
Other suburban bus lines are managed by private operators grouped in a consortium known as Optile (Organisation professionnelle des transports d'Île-de-France), an association of 80 private bus operators holding exclusive rights on their lines. There are approximately 9500 buses serving public transportation across the Paris region, all operators included.[1]
RATP operates:
) a circular transport service surrounding Paris's borders along the Boulevards des Maréchaux
towards the town hall of Aubervilliers or now-former line 528 before northern extension of 
from Saint Lazare train station to the town hall of Saint Ouen 
from Orly Airport to Juvisy train station, or 183 before extension of 
towards said airport)RATP bus lines operating mainly in the city proper of Paris, are named with a two-digit code number called "indice". Bus lines operated mainly in the suburbs are named with a three-digit number code.
RATP uses the numbers 20 to 96 for lines operated mainly in the city proper (1 to 19 are unused to avoid confusion with Metro lines) ; along with PC bus line (line 100) which runs along the Boulevard des Maréchaux section that is not yet covered by (Tramway lines 3a & 3b) . All this according to an organized scheme used since public transportation reorganization post-WWII.
The first digit represents the sector in Paris where the line's starting point is located:
The digit number represents the outermost arrondissement the line finishes (or crosses Paris' borders) in:
0 and 1 are used as "wildcards" for lines whose rightful indice is already taken, or for lines ending inside of Paris (40 or 91 for example).
A deep reorganization of the Paris bus network took place on April the 20th 2019. Although it didn't change the overall scheme mentioned above, it brought several irregularities, such as lines 20 21 & 24 no longer starting from Saint Lazare train station while brand new line 25 doesn't even approach it, line 30 now cut long before the Gare de l'Est, line 40 that doesn't even approach the Gare du Nord, or lines 71 & 77 that do not start from the center of Paris.
RATP operates 70 bus lines within the city of Paris proper, and a little over 200 bus lines in Paris suburbs.
In 2017, 1.15 billion journeys were made on RATP bus lines, including 382 million journeys on Paris lines and 768 million journeys on suburbs lines.[2]
