Conventionally laser beam shaping problems are defined by the required intensity and/or phase distribution in a single 2-D output plane, although recently there have also been examples for beam shaping solutions where the system output had to satisfy constraints in a small number of axially separated planes. For a number of application areas it is beneficial to be able to work with beams that have a particular intensity distribution that is specified in a 3-D volume. Laser material processing, optical microscopy and laser trapping (optical tweezers) are a few examples for these. We will discuss how diffractive optical elements can be used to generate beams with prescribed 3-D intensity profiles, with particular emphasis on techniques for the design of such diffractive optics. Practical examples will be given for the implementation of the diffractive optical elements using programmable spatial light modulators and for the application of the 3-D beams.