ETA is a terrorist organization that has murdered more than 800 persons since 1968. Its ideological origins are to be found both in the Basque nationalist doctrine of the early XXth century and in the extreme left wing ideology of the sixties. Its goal is the creation of an independent and socialist Basque State that would include Spanish and French territories. Born in the last years of the Franco dictatorship it thrived during the transition to democracy, winning the support of a 15% of the population in the Basque Autonomous Region. The Spanish counter-terrorist strategy, that has nearly achieved the final defeat of ETA, offers valuable experiences for other countries threatened by terrorism.