The quest for lepton number violation, represented primarily by
searches for neutrinoless double beta decay (0vbb), is a prominent probe of physics beyond the Standard Model. The new particle physics underlying any potential lepton-number-violating signal can be parametrized within the framework of effective field theory in terms of a set of higher-dimensional operators triggering a variety of distinct mechanisms. While it seems to be challenging to unravel the dominant source from the observation of 0vbb itself, the (non-)conservation of lepton number can be also tested in a variety of other experiments. After going over the phenomenological consequences of double-beta-decay searches and their limitations, I will discuss the complementary probes of lepton number violation and their interplay with 0vbb.