Planned since the 1960s, construction of the Metro was not officially launched until the late 1990s mainly because the city did not experience an urgent need for an underground system and lacked funding. Another factor was the construction works depth: being one of the oldest cities in Europe, Sofia contains many historical layers underneath its central core. The construction of the system began from the areas that experience the most of the traffic in the capital city, where the largest streams of passengers form, reaching up to 40,000 at rush hour.

      Currently there are two interconnected lines (27 stations) with a total length of 31 km (19 mi) connecting the highly populated districts of Lyulin - Mladost (Line 1 - Red) and Nadezhda - Lozenetz (Line 2 - Blue).