The Montclair-Boonton Line is a New Jersey Transit line with a complicated history that is the combination of three different branches of two original railroads. The line entered its current form when the Montclair Connection opened on September 30, 2002 between Bay Street and Walnut Street. This combined operations of the electrified (starting in 1930) Montclair Branch of the Morris & Essex Lines (ex-Lackawanna Railroad) with the infrequent and diesel (ex-Erie) Boonton Line that continued to Hoboken via three now abandoned stations at Arlington, Rowe Street, and Benson Street on a now abandoned route. On this same date in 2002 MidTOWN DIRECT Montclair trains entered service providing a one-seat ride from Montclair to New York-Penn Station for the first time instead of only from Hoboken from both branches and electrification was also extended from Bay Street to Montclair Heights and later to Montclair State University at Little Falls when that new station opened in phases in 2003 and 2004.

Current weekday service on the line is roughly hourly (or better during rush hours) MidTOWN DIRECT Montclair service between New York Penn Station and Montclair State University. Service beyond to Dover and Hackettstown (some service to Hackettstown, including reverse peak service and a midday round-trip runs via the Morristown Line) is operated via diesel trains to and from Hoboken in the peak-direction only, 5 Inbound trains leave from Hackettstown or Lake Hopatcong running via the Montclair Line between 5:05am and 8:23am, 9 return trains arrive (some terminate in Dover) between 3:30pm and Midnight. Until 2010 there was additional midday service with some diesel shuttle trains between Montclair State University and Dover, with passengers changing to MidTOWN DIRECT electric trains for service to Newark (transferring again to a Gladstone Branch train to reach Hoboken) and New York City.

Weekend service has been controversial in Montclair with residents worried about the impact of train horns on their quality of life, this meant that in modern times there was no service on the Montclair Branch or the Boonton Line, even after the Montclair Connection opened in 2002. Weekend service finally began on September 30, 2009 only as far as Bay Street, with electric trains (normally Arrow MU equipment) running every two hours only between Hoboken and Bay Street.