How To Get Istanbul ?
Turkey demands an official entry visa from the citizens of some countries. Before your departure to Turkey it is better to check with a Turkish Consulate in your country to determine if you need a visa. In some cases, you can obtain a visa upon arrival at Ataturk Airport.
For detailed information:

By Air
Almost all international airlines have convenient direct flights to Istanbul from all over the world.
Turkish Airlines, which has been carrying passenger and cargo since 1933, today has a fleet of 134 aircraft and flies to a total of 103 destinations, 26 domestic and 77 international. It has consolidated its position on the international platform by linking the Caucasian countries and the Turkish Republics in Central Asia, as well as the Middle Eastern and Asian countries, with Europe, Africa and North America; through the service network hub in Istanbul. Turkish Airlines is a member of star alliance.

By Road
The road network throughout Turkey is extensive, with motorways, dual carriageways and numerous three-lane highways. Drivers bringing cars into Turkey must show their registration documents and driving license at the point of entry. If arriving from Europe, visitors must have a Green Card (available from insurance companies) as well as appropriate insurance. Driving is on the right. Seat belts are mandatory and driving after consuming alcoholic drinks is prohibited. The speed limits are I20km/h on motorways, 90km/h on main roads and 50km/h in towns.

By Intercity Coach Services
Coach services to all parts of Turkey are reliable, reasonably priced and convenient. Istanbul's International Bus Terminal located in Esenler, about ten kilometers from the city center, serves all international and domestic lines. Most of the leading intercity coach companies provide free shuttle services from central Istanbul to the terminus. These leave a couple of hours before the scheduled departure time of the coaches from Siraserviler Caddesi in Taksim, which is also where the ticket offices are located. Visitors can book tickets here any time before departure.

Major European cities such as Frankfurt and Vienna are also well serviced by Turkish coach lines, and there are daily bus connections between Athens and Istanbul via Thessalonica.

By Rail
There are trains from Sofia, Belgrade, Bucharest and Budapest(connections from Munich and Vienna) to Sirkeci Station in Istanbul. Main services are:

There are two main stations in Istanbul: Sirkeci Station on the European and Haydarpaşa Station on the Asian side. These historic station buildings are nostalgic gateways to the city. Both stations are well equipped with restaurants, newspaper kiosks, waiting rooms and ATMs. Both stations are conveniently located. Haydarpaşa Station on the Asian shore is connected to the European shore by ferry to Karakoy, and Sirkeci Station is a short walk or taxi ride from Eminonu ferry terminals. Suburban trains also run from Sirkeci and Haydarpaşa stations.

By Sea
The Bosphorus Strait divides Istanbul's Asian and European shores. Central Istanbul and the historic walled city are on the European shore, which is itself divided by the natural harbour of the Golden Horn (Haliç). Tiny fishing boats and day cruisers share the Bosphorus with enormous international cargo ships, navy vessels, tankers and giant luxury liners from Europe. The two largest quays, Eminonu and Karakoy, are on opposite sides of the Golden Horn and linked by the Galata Bridge. Karakoy is where luxury cruise ships headed for the Aegean and Mediterranean dock, as well as smaller CIS vessels. Local ferry services mainly depart from Eminonu, Karakoy, Besiktas and Üskudar. International ferry services to Turkey;