A single ticket (the same kind used for all forms of mass transit in Paris)
is good for one trip between two points on one or more buses, trains, or
trams within the city. Things gets more complicated for rides within or
towards the suburbs, which may require several tickets and/or specific
point-to-point tickets. If you buy your ticket directly from the bus driver as
you board, the ticket is only good for one ride on that bus—you can’t make
any connections. The time between your first use of a ticket on a bus and
the last use of the same ticket on a bus must not exceed 90 minutes.
All of the buses in Paris are managed by the RATP. Bus routes in the
suburbs are often operated cooperatively by the RATP and local suburban
transportation authorities.
Unlike the Métro and RER, the bus lines do not stop completely during
the night. The Noctilien bus service continues with 31 lines all night long
in Paris and a few suburbs, during the period when the normal daytime
lines have stopped (from roughly 11 pm or so to 6 am).