Like building a Stradivarius violin, design of laser resonators is a work of art. Similar to the vibrations of sound in a violin, the vibration modes of light in a laser cavity are controlled by complex interaction of material properties and technical design. LAS-CAD GmbH has developed the package LASCAD to provide a quantitative understanding of this interaction, and to assist the engineer to analyze and improve design concepts for laser resonators. Though comprehensive experimental experience still will be necessary to develop lasers, computer simulation is about to become an important engineering tool in laser cavity analysis and design.