Microdisplays are considered to be an enabling technology for ultra-high resolution displays. Pixels can indeed be made very small using CMOS technology. Nevertheless, in multimillion pixel microdisplays, the die size becomes a limiting issue, because the optical field size of present day lithographic steppers, and consequently the resulting chip size, is limited to about 20x20 mm2. This paper shows how this limitation can be overcome using stitching techniques and discusses the resulting challenges in design as well as lithography. The partitioning of the schematics and the layout in stitchable modules is reviewed, as well as the definition of boundary conditions for these modules. The difficulties concerning design verification, and a virtual stitching procedure that can be helpful, are presented. From a technological point of view, the stepper job creation and the scribe line definition is described, as well as the positioning accuracy that is achieved. It is also shown that careful partitioning of the design can lead to a single stitchable mask set that allows the creation of microdisplays with several different resolutions. The paper is illustrated with results from the European Esprit project Mosarel, a project that has shown the feasibility of a 2560x2048 pixel microdisplay.