This is an introduction to the various techniques of inverting geophysical data into realistic models of the Earth. The various methods are given a unified treatment, from the simplest inversion using nomograms to the mathematically most advanced ones. The use of generalized linear inversion, non-linear optimization, statistical information theory as well as techniques using advanced functional analysis are all discussed. In addition, the error analysis, effects of correlation between model parameters, computational aspects, the geological relevance of models, general psychological aspects and pitfalls in inversion are also mentioned. The reader will find examples which cover all major disciplines of Solid Earth and Applied Geophysics. The book is intended for undergraduate students as a first introduction to geophysical inversion, but can also be used as a standard reference for scientists and geophysicists.