Known ignition coils have a high-voltage connection, a spring for electrically connecting the high-voltage connection to a spark-plug and an elastic protective jacket that surrounds the spring. The windings of the spring lie in a block against one another in a block section that faces the high-voltage connection and are interspaced in a spring section designed to contact the spark-plug. To permit the ignition coil with the elastic protective jacket to be pushed easily onto the spark-plug, said protective jacket is reinforced by the integration of two metal sleeves. However, the disadvantage of these sleeves is that they involve higher production costs and increase the diameter of the protective jacket. In addition, the sleeves reduce the flexibility of the protective jacket. In the ignition coil according to the invention, the rigidity of the protective jacket is increased without additional components, thus cutting production costs and reducing the diameter of the protective jacket. According to the invention, the end of the block section (15.1) of the spring (15), facing the spring section (15.2), is supported on at least one support shoulder (20) of the protective jacket (16).