An overall calibration theory for Multiport Network Analyzers (MNWA) is presented. A general algorithm is developed to exploit the redundancy inherent in MNWA selfcalibration. Linear dependency conditions given by using oneport or two-port standards to calibrate a MNWA are analyzed, by deriving novel criteria for multiport self-calibration. It is theoretically and experimentally demonstrated that an n-port test set can be calibrated by using only one two-port standard and one load. The excellent accuracy reached by means of this new theory opens new alternatives to a metrological qualification of MNWA for n-port device testing.