Okayama is an important stop on the Sanyo Shinkansen route. All shinkansen trains stop at Okayama for a brief time after that reinitiate his journey.
Nozomi provides the most frequent services, they operate on the entire shinkasen route; trains depart Tokyo every 20 minutes or so. Hikari Rail Star trains also take frequent runs, stopping in Okayama on runs among Osaka and both Kokura Station in Kitakyushu and Hakata Station in Fukuoka.
Also, the Hikari train goes out each hour from Tokyo to Okayama, but it takes a bit longer since the train stops at all stations after Nagoya.
If you don't get a Japan Rail Pass it is viable to travel cheaply overnight from Okayama to Matsuyama, Kochi and Fukuoka during University vacation periods using Moonlight Special Rapid services. These are very accepted and tend to get booked a month in advance.
Local trains also go northward several times daily to Yonago and Tottori Cities in Tottori prefecture and Matsue and Izumo Cities in Shimane prefecture. This interesting scenic trip over the mountain range takes about two hours.
Chugoku JR Bus offers an overnight bus service, the Kibi Dream from Tokyo Station and the Yokohama City Air Terminal (YCAT) to Okayama. The travel time lasts around 10 hours from Tokyo (¥10000 one way, ¥16600 round trip) and 9 hours from Yokohama (¥9700 one way, ¥16200 round trip).
Daytime buses controlled by Ryobi Bus depart hourly from Osaka Namba (three hours, ¥3060 one way, ¥5610 round trip), and 5 times daily from Kyoto (3 1/4 hours, ¥3500 one way, ¥6300 round trip).
Several airports such as Tokyo, Sapporo, Sendai, Kagoshima and Okinawa offer many flights towards Okayama. Among Okayama and Seoul, Shanghai, Dalian, Beijing and Guam exists direct flights too. Buses make a 40-minute run to the Okayama train station (¥680).