The Fourier synthesis technique of image formation has been in use in radio astronomy since the 1950's. Interferometric measurements provide values of the complex Fourier transform of a brightness distribution at a finite set of spatial frequencies, and it is required to reconstruct the brightness distribution. Originally, the reconstruction consisted simply of computing the inverse transform with the values at all unmeasured spatial frequencies set to zero. With good spatial frequency coverage, this often gives a satisfactory result. However, observations are often made with limited coverage. Also, the increasing sensitivity of radio telescopes has led to a demand for larger dynamic range in the images. There has therefore been an effort to develop improved imaging techniques; these are reviewed here.