We will begin with a discussion of why a single degree of freedom does not constitute a clock in itself. Once we understand what a clock is not, we will move on to explore the minimal constituents of a clock. We need clocks to measure time, since quantum mechanics does not provide us with an observable for it. In order to understand and investigate time-measuring devices in the quantum regime, we will introduce a model of a clock — the autonomous quantum clock — and demonstrate how thermodynamics influences its ability to keep time, as well as trade-off relations that follow from this relationship. We will also present experiments that hint towards a elemental nature of these trade-off relations and discuss how timekeeping is connected to the fundamental limitations of quantum technologies. Finally, we will conclude with a brief discussion of the latest findings and open questions.