A Russian rocket carrying the Venus Express lifted off from the Russian-leased Baikonur cosmodrome in Kazakhstan.
It will take about five months for the probe to reach Venus, the nearest planet to Earth. Once in orbit there, the Venus Express will explore the hot and dense atmosphere around the planet.
This is the European Space Agency's first mission to Venus. It cost about 220 million euros ($259 million).
The last mission to Venus was Magellan, launched by the American space agency NASA in 1989.