Over the past 15 years or so, numerous studies have sought to characterise how nuclear calcium (Ca²⁺) signals are generated and reversed, and to understand how events that occur in the nucleoplasm influence cellular Ca²⁺ activity, and vice versa. In this Commentary, we describe mechanisms of nuclear Ca²⁺ signalling and discuss what is known about the origin and physiological significance of nuclear Ca²⁺ transients. In particular, we focus on the idea that the nucleus has an autonomous Ca²⁺ signalling system that can generate its own Ca²⁺ transients that modulate processes such as gene transcription. We also discuss the role of nuclear pores and the nuclear envelope in controlling ion flux into the nucleoplasm.