Yūrakuchō Line through-running network

The network's connections were planned long before they opened. On 5 September 1968 the Teito Rapid Transit Authority — the predecessor of today's Tokyo Metro — and Seibu Railway exchanged a memorandum agreeing to run mutual through-services, aiming to link the planned Line 8 (the Yūrakuchō Line) with the Seibu Ikebukuro Line by around 1973. The line opened in stages from 30 October 1974, when the first section between Ikebukuro and Ginza-itchōme entered service. Through-running itself began on the Seibu side: on 1 October 1983 the Seibu Yūrakuchō Line opened between Kotake-mukaihara and Shin-Sakuradai, and trains started running through between the two railways — the first through-service of the network.

The Tōbu connection followed with the line's northwestern extension. On 25 August 1987 the segment from Eidan-narimasu (now Chikatetsu-narimasu) to Wakōshi opened, and through-running with the Tōbu Tōjō Line began at Wakōshi, with trains continuing to Kawagoeshi and, for depot-working services, Shinrin-kōen. The Yūrakuchō Line was completed on 8 June 1988 when the final section from Shintomichō to Shin-kiba opened. The Seibu link deepened in two further steps: on 7 December 1994 the Seibu Yūrakuchō Line was extended to Nerima and Seibu's own trains began running through, and on 26 March 1998 the Seibu Yūrakuchō Line was fully double-tracked, allowing full mutual through-running onto the Seibu Ikebukuro Line as far as Hannō — finally realising the connection first agreed in 1968, twenty-five years after the original target.

A distinctive feature of the network is the corridor it shares with the Fukutoshin Line. Under Tokyo's transport plans the Wakōshi–Kotake-mukaihara section is officially Line 13 — the Fukutoshin Line — while the section south of Kotake-mukaihara is Line 8, the Yūrakuchō Line proper; the northern stretch was nonetheless signed as the 'Yūrakuchō Line' to keep service continuous and avoid confusing passengers. A precursor service known as the 'Yūrakuchō New Line', which opened between Kotake-mukaihara and Ikebukuro on 7 December 1994, was absorbed into the Fukutoshin Line when that line opened on 14 June 2008; from then on Yūrakuchō Line and Fukutoshin Line trains have shared the tracks and station facilities between Wakōshi and Kotake-mukaihara. Because the two lines share this corridor, Tōbu Tōjō and Seibu trains can reach both the Yūrakuchō Line toward Shin-kiba and the Fukutoshin Line toward Shibuya from the same junction at Kotake-mukaihara.

The line's ownership passed from the Teito Rapid Transit Authority to Tokyo Metro on 1 April 2004 with the Authority's privatisation. Later additions to the network include the reserved-seat S-Train, which launched network-wide on 25 March 2017 (Saturday) with weekday Yūrakuchō Line services between Toyosu and the Seibu Ikebukuro Line beginning 27 March 2017 (Monday). Through-running across the network continues today at both the Tōbu and Seibu ends, and remains the defining characteristic of the Yūrakuchō Line's daytime operation.

Through-running operates at the northern end on two sides. From Wakōshi, trains through-run onto the Tōbu Tōjō Line to Kawagoeshi (and to Shinrin-kōen in the morning and evening). From Kotake-mukaihara, trains through-run via the Seibu Yūrakuchō Line onto the Seibu Ikebukuro Line to Kotesashi (with some morning and evening services reaching Hannō); some Seibu through-trains run as semi-express, rapid or rapid-express within the Seibu lines, changing service type at Kotake-mukaihara. The reserved-seat S-Train runs on weekdays between Toyosu and the Seibu Ikebukuro Line. The Wakōshi–Kotake-mukaihara section is shared with the Fukutoshin Line, so Shin-kiba-bound Yūrakuchō trains and Shibuya-bound Fukutoshin trains both use this corridor.

• 1968On 5 September 1968 the Teito Rapid Transit Authority (the predecessor of today's Tokyo Metro) and Seibu Railway exchanged a memorandum on mutual through-running, fixing the intent to connect the planned Line 8 (Yūrakuchō Line) with the Seibu Ikebukuro Line; full Seibu Ikebukuro Line through-services were initially targeted for around 1973 but did not arrive until much later.
• 1974On 30 October 1974 the Yūrakuchō Line opened its first section between Ikebukuro and Ginza-itchōme, operating at first with five-car trains; the line was named through a public competition that drew 30,591 entries.
• 1983On 1 October 1983 the Seibu Yūrakuchō Line opened between Kotake-mukaihara and Shin-Sakuradai and through-running between the Yūrakuchō Line and Seibu began, the first through-service of the network.
• 1987On 25 August 1987 the northwestern extension from Eidan-narimasu (now Chikatetsu-narimasu) to Wakōshi opened and through-running with the Tōbu Tōjō Line began; Tōbu depot-working trains ran as far as Shinrin-kōen while most through-trains terminated at Kawagoeshi.
• 1988On 8 June 1988 the final section between Shintomichō and Shin-kiba opened, completing the Yūrakuchō Line between Wakōshi and Shin-kiba.
• 1994On 7 December 1994 the 'Yūrakuchō New Line' opened between Kotake-mukaihara and a new Ikebukuro terminal, and on the same day the Seibu Yūrakuchō Line was extended to Nerima, allowing Seibu rolling stock to begin running through onto the network.
• 1998On 26 March 1998 the Seibu Yūrakuchō Line was fully double-tracked and full mutual through-running with the Seibu Ikebukuro Line began, extending through-services as far as Hannō — the connection first envisaged in 1968.
• 2008On 14 June 2008 the Tokyo Metro Fukutoshin Line opened; the Wakōshi–Kotake-mukaihara stretch became a corridor shared with the Fukutoshin Line and the former Yūrakuchō New Line section was absorbed into the Fukutoshin Line.
• 2017Seibu's reserved-seat S-Train limited-stop service launched network-wide on 25 March 2017 (Saturday); weekday Yūrakuchō Line services, running between Toyosu and the Seibu Ikebukuro Line and stopping within the Yūrakuchō Line only at Iidabashi and Yūrakuchō, began on 27 March 2017 (Monday).
• 2022On 6 August 2022 one-person operation was extended to the Kotake-mukaihara–Shin-kiba section, completing one-person operation across the whole Yūrakuchō Line.