Localized optical fields exert both conservative and non-conservative forces on polarizable objects. These forces can be used to control and manipulate the motion of atoms, molecules or nanoparticles. In this presentation I discuss our experiments with optically levitated nanoparticles in ultrahigh vacuum. Using active feedback control we cool the particle’s center-of-mass motion to near strand-still and measure its quantum zero-point energy. A laser-trapped particle in high vacuum defines a harmonic oscillator with ultrahigh quality factor. I will show that its damping is dominated by photon recoil heating. A levitated nanoparticle is a model system for studying non-equilibrium processes, nonlinear interactions, and ultrasmall forces.