This thesis deals with test signal probing and fixturing techniques for wideband multiport measurements in digital packaging in the frequency range from a few MHz to 50 GHz. Three different signal launch techniques are investigated in time and frequency domains. At first, the performance of the coaxial surface mounted connector launch is explored in case of crosstalk measurements in a backplane connector via pin field. In the next step the recessed probe launch technique is briefly presented. After that the main focus is on the results obtained in recent investigations with respect to the launch calibration, application to measurements of embedded multilayer structures and modifications to improve the launch bandwidth. Finally, the concept of a novel multiport probing fixture is presented and its electrical performance explored. Using a simple two-tier calibration procedure, the effect of the probing fixture on measurements of dense via array structures is reduced and the results obtained are validated with microprobe based measurements. Based on 3D full-wave electromagnetic modeling, suggestions for layout optimization are made which will be needed to extend the applicability of these techniques to data rates of 20 Gbit/s and beyond.