Missing Partner Mechanism in SO(10) Grand Unification

We present a new possibility for achieving doublet–triplet splitting naturally in supersymmetric SO(10) grand unified theories. It is based on a missing partner mechanism which is realized with the 126 + 126 Higgs superfields. These Higgs fields, which are also needed for generating Majorana right–handed neutrino masses, contain a pair of color triplets in excess of weak doublets. This feature enables us to remove the color triplets from the low energy spectrum without fine–tuning. We give all the needed ingredients for a successful implementation of the missing partner mechanism in SO(10) and present explicit models wherein the Higgs doublet mass is protected against possible non–renormalizable corrections to all orders. We also show how realistic fermion masses can be generated in this context.