Chapter 2 gives an introduction to the all pervasive seismic noise (section 2.1), its measurement, and instrumental and computational analysis (section 2.2). The subsequent sections give an introduction to seismic isolation by means of mechanical oscillators, such as harmonic oscillators (section 2.3) and a selection of low-frequency oscillators (section 2.4). Examples of low-frequency oscillators implemented as seismic isolators in gravitational wave detectors (section 2.5) are given.