This second edition enables readers to design lens systems for focusing beams of charged particles that have useful characteristics. The book covers the basic theory of the motion of charged particles in electrostatic fields and describes several methods for the calculation of the potential and field distribution for various electrode geometries. It emphasizes the Bessel function expansion method and the nine-point implementation of the finite difference method. The accompanying disk provides a suite of computer programs (LENSYS for MS-DOS) intended for practical use in the design and analysis of systems using round lenses with apertures or cylindrical elements.