Sounder Commuter Rail is the commuter railway that runs limited and primarily peak direction rush hour service on two lines either north and south of Seattle. The system uses Bombardier BiLevel Cars and F59PHI Locomotives operated under contract by BNSF which is also the host railroad. The fleet is maintained by Amtrak during the midday layovers in their Seattle Coach Yard.

In 2014 the main Sounder S (South) Line operated 7 peak direction trips (5 of these, those that don't return to Seattle for reverse-peak trips, are extended to Lakewood), plus 2 reverse peak trips and service has been gradually increased from just two round-trips in 2000. Its trains can be up to 7 coaches long. As of 2024 there are 10 peak-direction and 3 reverse-peak direction round-trips between Seattle and Tacoma, there are 7 daily trips to and from Lakewood, withe one of the 3 morning reverse-peak trips extended to Lakewood, allowing a same-day return from Lakewood by train 1 hour later (this is a mid-morning inbound trip leaving Lakewood at 10:11am).

The Sounder N Line is newer and has much less ridership, using generally just three car trains on four peak direction round-trips. Trains operate in push-pull configuration with the locomotive always at the southern end of the train (so pushed north, pull south) for both lines. It began operations in December 2003 with just one round-trip. As of 2024, this peak of four trips in the peak direction rush hour has been reduced to just 2 round-trips per weekday due to COVID-19 related reductions in daily commuters. Monthly pass holders can take advantage of the Rail Plus program and ride the two Amtrak Cascades (not the Empire Builder) that operate north of Seattle (this is not applicable between Seattle and Tacoma). Sounder train service runs weekdays only except for special Sunday Football Game Service for Seahawks Games (as of 2014 3 South trips, one inbound even runs express, 2 North trips), and some weekend Sounders FC soccer matches, and Mariners Games.