The Saikyo Line (埼京線, Saikyō-sen) connects southern Saitama Prefecture with Akabane, Ikebukuro, Shinjuku, Shibuya and Osaki.
Between Ikebukuro and Osaki, the Saikyo Line runs parallel to the Yamanote Line, but stops only at Shinjuku, Shibuya and Ebisu Stations. North of Tokyo, some trains run as far as Kawagoe.
While the Saikyo Line technically ends at Osaki Station, many trains on the Saikyo Line continue to run on the Rinkai Line from Osaki to Odaiba, before terminating at Shin-Kiba. Note, that the Rinkai Line is not owned by JR, which means that the Japan Rail Pass and similar JR tickets are not valid on it.
Below are more details about the stations of the Saikyo Line in their actual order.
Ikebukuro is one of Tokyo's largest shopping and entertainment districts. Several suburban train lines commence at Ikebukuro Station.
Shinjuku Station is Japan's busiest train station. It is located in the middle of the large Shinjuku business, entertainment and shopping district. Many suburban train lines commence at Shinjuku Station.
Shibuya is a large shopping and business district particularly popular among the younger generations. Several suburban train lines commence at Shibuya Station.