An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C-H activation mediated by the germylene (germanediyl) Ge(Ar-Me6)(2) (Ar-Me6 = C6H3-2,6(C6H2-2,4,6-Me-3)(2)) showed that it proceeded by initial MeNC adduct formation followed by an isomerization involving the migratory insertion of the MeNC carbon into the Ge-C ligand bond. Addition of excess MeNC led to sequential insertions of two further MeNC molecules into the Ge-C bond. The insertion of the third MeNC leads to methylisocyanide methyl group C-H activation to afford an azagermacyclopentadienyl species. The X-ray crystal structures of the 1:1 (Ar-Me6)(2)GeCNMe adduct, the first and final insertion products (Ar-Me6)GeC(NMe)Ar-Me6 and (Ar-Me6)GeC(NHMe)C(NMe)C(Ar-Me6)NMe were obtained. The DFT calculations on the reaction pathways represent the first detailed mechanistic study of isocyanide oligomerization by a p-block element species.