Efficient methods of implementing a digital interpolation beamformer which utilize interpolation filters to reduce the rate at which the outputs of the array elements are sampled are discussed for both lowpass and bandpass signals. The bandpass case is an important application since the data can be sampled at a low rate consistent with the bandwidth of the signal. In both applications interpolation is performed efficiently using finite impulse response (FIR) digital filters. The advantages of an FIR filter over recursive filter implementations are presented. The interpolation filter thruput, which depends upon whether the interpolation is performed at the beamformer input or output, is shown to be related to the size of the array and beam steering requirements. However, the interpolation is usually performed most efficiently at the beamformer output for bandpass applications which require the modulation of the sampled signals. Efficient location of the modulation is also addressed. Examples of beampatterns are presented for digital interpolation beamforming and compared to those obtained with synchronous and nonsynchronous beamforming techniques.