Historical development of seismology; harmonic oscillator; waves on a string; coupled oscillators; stress and strain; elastic wave equation; representation theorems; P and S waves, potentials, P–SV and SH decomposition; ray theory and Fermat’s principle; basics of ray tomography; plane waves, boundary conditions, reflection and transmission; seismic anisotropy; intrinsic attenuation; Rayleigh and Love waves, dispersion, phase and group velocities; Lamb’s problem; scattering and Born approximation; basics of full waveform inversion; passive seismic imaging and interferometry; normal modes of the Earth: spheroidal and toroidal modes, eigenfrequencies, mode splitting.