Patent protection is legally capped at twenty years from filing, yet the effective duration varies widely because patent rights may cease for multiple reasons over their life cycle. A substantial share of patents terminates early due to procedural and legal terminal events, while a non-negligible fraction survives up to the statutory term. Against this background, the first objective of this thesis is to identify the end of patent protection in administrative data by constructing a patent-level “expiration” date, which is not directly recorded as a single variable in the EPO Register. The second objective is to address the core research question of whether, and to what extent, technological relevance explains heterogeneity in patent term and predicts patent lapse.