The Raritan Valley Line is what remains of service on the Central Railroad of New Jersey's Main line. Service on this line used to originate at the Communipaw Terminal in Jersey City with connecting ferry service to New York City, which has been preserved (no longer served by the railroad) in Liberty State Park. Today this historic terminal is where passengers can board ferries from New Jersey to visit the Statue of Liberty and Ellis Island.

In April 1967 train service was rerouted via the Aldene Connection onto the Lehigh Valley Railroad and via the Hunter Connection onto the Northeast Corridor and into Newark Penn Station, where all trains terminated with connections to Pennsylvania Railroad trains (today's Northeast Corridor and North Jersey Coast Line trains) and Hudson & Manhattan Railroad (today's PATH trains) into New York City. Until 1978 Scoot shuttle service operated along the former CNJ now abandoned mainline between Cranford and Bayonne (via the now-abandoned but restored into a restaurant historic Elizabeth Broad Street station). On the western end of the line service originally extended to Phillipsburg Union Station (and the CNJ trains ran as far as Easton and other points in Pennsylvania in earlier years) but service was discontinued and cut back to High Bridge in December 1983, with the line now abandoned.

Limited eastbound train service (the majority of Raritan Valley Line trains continue to terminate in Newark as they did in 1967) was extended in 1991 along the Waterfront Connection, to Hoboken. For example, in the mid-2000s every other Weekend train was extended to Hoboken. Today there is just one AM-rush hour inbound train that arrives at 6:29am with no return service from Hoboken. In March 2014, select weekday non-rush hour weekday and evening trains were extended into New York Penn Station using dual-mode ALP45DP locomotives, no service into New York is provided during rush hours due to capacity constraints caused by the just two-track North River Tunnels and on weekends when only one tube of the North River Tunnels is in service to allow for maintenance on the other tube.

Today's service on the Raritan Valley Line, consists of core service operating hourly or better on weekdays and weekends between Newark-Penn Station and Raritan. On weekdays 7 trains are extended to originate (while 10 trains terminate) in High Bridge, with no service west of Raritan on weekdays. 8 non-rush hour round-trip trains per weekday, 5 during middays (originating and terminating between 10:00am and 3:00pm), 3 during evenings (between 8:00pm and 11:00pm) are extended eastbound into New York Penn Station, stopping at Secaucus Junction, reversing in New York Penn station after short layovers. On Weekends, hourly service is provided between Newark and Raritan only. All train service is provided using Bombardier Multilevels using GP40PH-2 or Alstom PL42AC diesel locomotives, with dual-mode ALP-45DP locomotives used by the direct trains into New York.