The Frankston line is a commuter railway line in the city of Melbourne, Victoria, Australia. Operated by Metro Trains Melbourne, it is the city's third-longest metropolitan railway line, at 42.7 kilometres (26.5 mi). The line runs from Flinders Street station in central Melbourne to Frankston station in the south-east, serving 28 stations via South Yarra, Caulfield, Moorabbin, and Mordialloc. The line continues to Stony Point on the non-electrified Stony Point line. The line operates for approximately 20 hours a day with 24 hour service available on Friday and Saturday nights. During peak hour, headways of up to 5 to 10 minutes are operated with services every 10–20 minutes during off-peak hours. Trains on the Frankston line run with a two three-car formations of Comeng, Siemens Nexas, and X'Trapolis 100 trainsets.

Metro Trains Melbourne, often known simply as Metro, is the operator and brand name of train services on the electrified metropolitan rail network serving the city of Melbourne, Victoria, Australia. It is the largest urban rail network in Australia, with 17 lines and 221 stations across 405 km (252 mi) of railways, and the second busiest network in Australia, with a patronage of 99.5 million as of 2021–2022.