When an atomic gas is cooled to temperatures just above absolute zero, the atoms lose their individuality and the whole ensemble starts to behave as if it were one big quantum particle. In atomic gases, this `Bose-condensed state’ was first created in 1995. Bose condensates have since revolutionized cold atom physics and now form the starting point of the vast majority of experiments. In this talk I will discuss some of the most intriguing and distinguishing features of cold atom systems. I will show how they enable the study of fundamental and sometimes puzzling features of quantum physics and its relation to the everyday world. Furthermore, I will examine applications to quantum computing and as direct quantum simulators that may provide novel insights into the behaviour of ordinary matter.