The UCI ProTour is the series of races for the top cycling teams. The Continental circuits are for teams that are not so good.
Some teams, such as Team Milram, have one team on the ProTour, a team of younger riders on the continental circuit as well as being linked with U23 teams. In this way teams can spot talented riders.
There are five circuits, one each for
Usually organisers of a ProTour event can invite one or two teams from the continental circuit to compete. Also a ProTour team might decide to compete in a continental circuit race