Vacuum discharges are one of the main limiting factors for CLIC; and although sparks and arcs are present in our everyday life since thousands of years, the phenomenon of vacuum discharges is surprisingly poorly understood. In the talk, a review of ongoing experimental and theoretical research in the field will be given, including results from the 'DC spark setup' and a multi-scale model of vacuum discharges describing amongst others possible trigger mechanisms, plasma build-up, and resulting surface damage. The second part of the talk will focus on latest results concerning plasma build-up, obtained with a two-dimensional particle-in-cell code written for this purpose.