Micro-X-ray fluorescence offers the possibility for a position- sensitive and non-destructive analysis that can be used for the analysis of non-homogeneous materials and layer systems. This analytical technique has shown a dynamic development in the last 15 years and is used for the analysis of small particles, inclusions, of elemental distributions for a wide range of different applications both in research and quality control. The first experiments were performed on synchrotrons but there is a requirement for laboratory instruments which offers a fast and immediate access for analytical results. The book discuss the main components of a μ-XRF instrument and the different measurement modes, it gives an overview about the various instruments types, considers the special requirements for quantification of non-homogeneous materials and presents a wide range of application for single point and multi-point analysis as well as for distribution analysis in one, two and three dimensions.