Quantum fluids have emerged from scientific efforts to cool matter to colder and colder temperatures, representing staging posts towards absolute zero (Fig. 1.1). As a macroscopic manifestation of quantum mechanics they have contributed to our understanding of the quantum world, captivating and intriguing scientists with their counter-intuitive non-classical properties, and are increasingly finding applications in quantum technologies. Here we summarize the background of the two main quantum fluids to date, superfluid helium and atomic Bose-Einstein condensates.