Electromagnetic wave scattering from multiple rectangular apertures in a thick conducting screen is studied. The Fourier-transform and mode-matching technique are used to obtain simultaneous equations for the modal coefficients. The simultaneous equations are solved to represent the scattered and transmitted fields in series forms which are suitable for numerical computation. The numerical computations are performed to illustrate the aperture transmission and scattering behaviors in terms of aperture size, incident angle, and frequency. The effects of the finite number of apertures on the transmission characteristics are discussed.