In the early 1960s the concept of the sub-surface tramway was finally accepted and on 9 August 1966 the actual building of its first station (Hlavní Nádraží) started. Therefore this station's design reflects partly the original intention to build and underground tramway. However, next year a substantial change in the concept came, as the government decided to build a "true" metro system instead of an underground tramway. It was mainly because such metro systems were "fashionable" in the Soviet Union and there was a political decision to import the soviet metro trains, as you can read here. Thus, during the first years, the construction continued while the whole project was conceptually transformed. The regular service of the first nine-stations section of line C between Sokolovská (now Florenc) and Kačerov stations began operating on 9 May 1974, with a depot at Kačerov.
Construction of next sections continued then quite rapidly. On 12 August 1978 the first section of line A was opened with seven stations in total between Dejvická and Náměstí míru, meeting line C at Muzeum, which became the first transfer station. While all stations on line C had been built using the cut-and-cover method, on line A there were the first deep level bored stations (Náměstí míru with the depth 52 m being the deepest metro station in Prague up to now). In 1980 two extensions were copmleted at both lines: Line A thus reaching Želivského in the east and line C Kosmonautů (now Háje) in the southeast. The latter extension with four stations in total serves a large suburb consisting of high density housing estates called Jižní Město - "Southern Town" in Czech, which is the largest and densest housing estate in the Czech republic. Another extension of line C was opened in 1984 and reached Nádraží Holešovice. Finally, on 2 November 1985, the first seven-stations section of line B opened with termini at Smíchovské nádraží and Sokolovská, thus forming the triangle of the three transfer stations (the new ones were Můstek with line A and Sokolovská (now Florenc) with line C).
In the following years, except two stations added to line A in the east, primarilly line B was extended. These two new stations on line A were Strašnická (opened 1987) and Skalka, which was interesting, because it was built in 1990 along the already operational tracks from the then terminus Strašnická to a depot in Hostivař.
The first extension of line B in 1988 from Smíchovské nádraží reached Nové Butovice in the west. The next one in 1990 added four more stations in the east, with a new terminus at Českomoravská. Another extension was put into service in 1994. It goes to the west from Nové Butovice to Zličín and together with it, a new depot for line B was built in Zličín (before that, whole line B had been served from the Kačerov depot on line C). The last extension of line B reached Černý Most in the east and was opened in 1998. There were four intermediate stations, but two of them were to be completed only later. Thus the Hloubětín station was opened in 1999 and Kolbenova in 2001. At that time, line B was completed and there would be probably no more extensions of it during the following decades.
In the meantime, the old Russian and slowly wearing out trains are being reconstructed and replaced. The renewal of the rolling stock should be completed by 2007. You can read more about it in the rolling stock section.
In August 2002, the metro suffered disastrous flooding that struck parts of Bohemia and other areas in Central Europe. 19 stations were flooded: Malostranská, Staroměstská, Můstek and Muzeum on line A; Smíchovské nádraží, Anděl, Karlovo náměstí, Národní třída, Můstek, Náměstí Republiky, Florenc, Křižíkova, Invalidovna, Palmovka, Českomoravská and Vysočanská on line B; Nádraží Holešovice, Vltavská and Florenc on line C. It caused partial collapse of the transport system in Prague, the metro lines had to be substituted by trams and buses. The affected sections of the metro stayed out of service for several months, the last stations (Křižíkova and Invalidovna, located in the most damaged area - Karlín) reopened on 22 March 2003. Small silver plates have been placed at some stations to show the water level during the event. The costs of the recovery was around 7000000000 CZK (approximately 250 million ).
A northern extension of the line C was opened on 26 June 2004, with two more stations, Kobylisy and Ládví. Notable is the way that the new tunnels were built under the Vltava river. A unique "ejecting-tunnels" technology had been chosen to underpass the river. First, a trench had been excavated in the riverbed and the tunnels had been concreted in the dry docks on the riverbank. Then the docks had been flooded, and the afloat tunnels were moved as a rigid complex to their final position, sunk, anchored and covered.
In the May 2006 a small extension of line A to the east was opened. The extension includes one new station, Depo Hostivař, which is placed in a depot.
Another extension of line C was opened on 8 May 2008. There are three new stations: Střížkov, Prosek and Letňany.
There are further projects to start building a completely new line, the D line, represented by the blue color, afterward. It should connect the centre to the southern parts of the city and go from Hlavní nádraží through the Nusle quarter down to the Krč, Libuš and Písnice suburbs in the south. If the project goes well, the first sections of the line will begin operation around 2013.