The Lilydale railway line is a commuter railway line operating between Flinders Street in the Melbourne central business district and Lilydale through Melbourne's eastern suburbs including Richmond, Cremorne, Burnley, Hawthorn, Hawthorn East, Camberwell, Canterbury, Surrey Hills, Mont Albert, Box Hill, Blackburn, Nunawading, Mitcham, Ringwood, Ringwood East, Croydon, Mooroolbark, and Lilydale. It is part of the Melbourne rail network operated by Metro Trains Melbourne.
The Lilydale line runs through Melbourne's eastern suburbs across mostly gentle hills (but with some steeper sections near the end of the line), having few straight or level sections. Earthworks are significant, with deep cuttings at Hawthorn, Camberwell, Box Hill, Heatherdale and near Croydon. Around Glenferrie and Auburn the line has been raised above the surrounding area on an embankment to avoid level crossings of several roads. All but two level crossings have been eliminated between the city and Ringwood (Union Road at Surrey Hills and Mont Albert Road near Mont Albert). In 2010 grade separation removed the level crossing at Springvale Road, Nunawading, previously a major bottleneck. Grade separation removed the level crossings at Rooks Road and Mitcham Road, at Mitcham, in January 2014. Further grade separation works has also removed the level crossings at Blackburn Road at Blackburn station, and at Heatherdale Road at Heatherdale station.
From near Richmond, there are four tracks to Burnley where the Glen Waverley line branches off. From Burnley, the line is triplicated to Box Hill, then duplicated to Mooroolbark, while the final section between Mooroolbark and Lilydale is single track. After Lilydale station is a closed railway line that extends to Healesville.
Automatic Block Signalling applies throughout the line. The centre track on the triple-track section is signalled for bidirectional operation and is used for up trains in the morning and down trains at other times.
Terminating facilities are provided at Burnley (although inconvenient and not normally used), Camberwell, Box Hill, Blackburn, Ringwood and Mooroolbark, as well as Lilydale. Terminating facilities were once provided at Mitcham, however they were abolished during the grade separation and rebuild of the station during January 2014. Stabling facilities are provided at Burnley (adjacent to the Glen Waverley branch), Camberwell, Ringwood and Lilydale.
The line from Richmond to Hawthorn was opened initially to a temporary terminus at Pic Nic, just short of the Yarra River, in September 1860, and to Hawthorn in April 1861. It was extended to Camberwell in April 1882, then to Lilydale on the first day of December of that year.
Duplication from East Richmond to Hawthorn occurred about a week after the Lilydale extension opened, and a fortnight (two weeks) later, the same section was converted to Double Line Block Telegraph safeworking, and the section from Hawthorn to Camberwell had Staff and Ticket working implemented.
In May 1885, Hawthorn to Camberwell was duplicated and converted to Double Line Block Telegraph. Duplication was extended to Box Hill in December 1888.
Automatic signalling was introduced from December 1907 with the conversion of the section from East Richmond to Hawthorn to semi-automatic signalling, followed by Richmond to East Richmond being converted to automatic signalling in August 1919, East Richmond to Camberwell in two stages both in October 1922, and Camberwell to Canterbury the following month.
Electrification took place between Flinders Street and Box Hill in December 1922, and extended to Ringwood the following month, then to Croydon in November 1925 and finally to Lilydale in October 1925.
Conversion to automatic signalling resumed in April 1927 with the conversion of Canterbury to Surrey Hills, followed by Surrey Hills to Box Hill in October 1929.
The section from Croydon to Mooroolbark was duplicated in 1957, creating a long passing loop on this otherwise single-line section beyond Ringwood. The section from Mooroolbark to Lilydale remains a single track.
Automatic signalling conversions resumed in July 1958 with the section from Box Hill to Blackburn, followed by Mitcham to Ringwood in September of that year, and Blackburn to Mitcham in November 1960.
Hawthorn to Camberwell was triplicated in December 1963, and the triplication was extended to East Camberwell in November 1964. Richmond to Burnley was quadruplicated in 1966/67, and triplication was extended to Box Hill in December 1971, followed by Burnley to Hawthorn in August 1972. This left a short section of double track on the up side of Richmond, but this was quadruplicated with the construction of a flyover in 1973.
Ringwood to Croydon was converted to automatic signalling in November 1973 and duplicated in June 1984. Mooroolbark to Lilydale was converted to automatic signalling in June 1985.
The Comeng trains were introduced to the Melbourne railway system in 1981. Initially, along with the Lilydale line, they were only allowed to operate on the Alamein, Belgrave, Dandenong and Glen Waverley lines, due to the width of the trains (3.05 metres).
The level crossing at Heatherdale Road, Mitcham was removed in 2017 along with building the new Heatherdale Station. The crossing was removed by lowering the line under Heatherdale Road. The station was rebuilt on the east side of the road. The level crossing at Blackburn Road in Blackburn was also removed in 2017, with the rail line lowered under Blackburn Road. The project included major enhancements to the existing Blackburn Station for better integration with Blackburn Village. A new walking and cycling path between Blackburn and Nunawading was built.  The level crossings at Union Road, Surrey Hills and Mont Albert Road, Mont Albert will be removed along with the level crossings at Manchester road, Mooroolbark and Maroondah Highway, Lilydale.
The Lilydale and Belgrave lines are notable for a variety of express services. Weekday services run express between Richmond and Box Hill between 6 am and 7 pm on weekdays. Most express services making stops at Glenferrie and Camberwell stations, and some stopping at Surrey Hills station. Express trains are supplemented by Blackburn services stopping all stations between Richmond and Blackburn, with a select number of these services skipping East Richmond and Laburnum. A select number of peak hour services also run as express trains beyond Box Hill, running express between Box Hill, Blackburn, Mitcham and Ringwood. Peak hour express trains are supplemented by Alamein line services stopping all stations between Flinders Street and Camberwell. A limited number of services terminate at Mooroolbark or Ringwood.
Weekend services on the Lilydale line run direct from Richmond to Flinders Street and then commence outbound journeys via the City Loop, stopping all stations to Lilydale except East Richmond. Early morning weekend services run direct to and from Flinders Street, stopping all stations including East Richmond.
Belgrave and Lilydale line trains alternate as shuttles from and to Ringwood during early morning and late night services all week.
Bold stations are termini, where some train services terminate; italic stations are staffed; and stations with an asterisk (*) are manned only during morning peak.
Lilydale railway line
All weekday morning services operate via the City Loop to Flinders Street in anticlockwise direction. On weekday afternoons, most services travel direct to Flinders Street before travelling via the Loop with some Blackburn all-station services running back to Richmond without going through the City Loop. Weekend services travel direct to Flinders Street before running via the Loop. This does not include night services. 
There were proposals for a station between Lilydale and Mooroolbark near the intersection of Hull and Mooroolbark roads, named Cave Hill, it has been finalised that the station will not be built in the mid term future. However, a future development in the area would require a railway station. In the PTV Network development plan, released 2012, duplication between Moroolbark and Lilydale was proposed along with an intermediate station. 
The level crossings at Surrey Hills and Mont Albert are planned to be removed. There are plans to duplicate the tracks between Mooroolbark and Lilydale, and to quadruplicate the section between Burnley and Box Hill.
On 12 May 2010, a X'Trapolis 100 ran off the end of the tracks and into a fence in the Ringwood stabling yard.
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- "Blackburn Road, Blackburn | Level Crossing Removal Project". levelcrossings.vic.gov.au.
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- "Mont Albert Road, Mont Albert | Level Crossing Removal Project". levelcrossings.vic.gov.au.
- "Manchester Road, Mooroolbark | Level Crossing Removal Project". levelcrossings.vic.gov.au.
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