ExperimentalRotationof Helium II studies on rotating Helium II led to the discovery of quantized vortices, namely, vortex lines whose circulation is \(\kappa = \frac{h}{m_4}\) , where h is Planck’s constant, and \(m_4\) the mass of one helium atom ( \(\kappa \simeq 9.97\) 10 \(^{-4}\)  cm \(^2\) /s) [1–5]. In this chapter, we consider rotating helium, and in Chap.  6 we will consider combined rotation and heat transport, two sources of quantum vorticity interacting in a non-additive way. Quantized vortices also appear in turbulent superfluid helium, which will be explored in more detail in Chap.  5 [4, 5], and in superconductors. They were predicted for the first time by Onsager in 1949, in connection with rotating superfluid helium, interpreting them as topological defects. Rotating superfluids have not only a fundamental interest, but are also found in rotating neutron stars, where a fraction of the system is in superfluid form.