'Digital In-line Holographic Microscope for Ice Crystals' originates from the dissertation of Peter Amsler. The purpose of the doctorate was to improve the knowledge of the optical properties of cloud constituents and hence of the clouds themselves. A special interest lied and still lies on the different habits of ice crystals and their ability to depolarise light. Therefore, there was a need for an imaging system capable of displaying 2 or even 3 D shapes of hydrometeors. In this work, the way from general considerations towards the building of the instrument is described in the first 4 chapters. Chapter 5 depicts the necessary steps towards testing thoroughly the imager and results displaying the role of ice crystal shape and number distributions in a certain environment are shown in chapter 6 and 7. The last sections comprise a short consideration about the multidimensional characteristic of holographic imagers.