We have used ab initio quantum-mechanical methods to study the electronic states of germavinylidene, H2C=Ge, and the isomerization of ground-state singlet germavinylidene to the less stable trans-bent germyne isomer, H-C-=Ge-H. The electronic states of germavinylidene that we have studied are the ground (1)A(1) state, the (1)A(2) and (3)A(2) states, involving a pi to p(y) transition, and the B-1(2) and B-3(2) states obtained from the ground state by an n to p(y) transition. We have also investigated the ground state of the germavinylidene anion, and the two lowest-lying cation states. Our predicted (B) over tilde B-1(2)-(X) over tilde (1)A(1) excitation energy agrees well with the recent experimental value. The geometries of the B-1(2) and B-3(2) states of germavinylidene might he expected to be similar, but they by 0.1 Angstrom in the Ge-C bond length and 12 degrees in the H-C-H bond angle. This results from the large electron repulsion between the unpaired electrons in the B-1(2) state, which essentially reside on the same atom. The anomalously low value of the CH2 rocking frequency in germavinylidene is rationalized as a second-order Jahn-Teller effect, Finally, the trans-bent germyne isomer requires 7 kcal mol(-1) to isomerize to the germavinylidene isomer, which is 43 kcal mol(-1) more stable than germyne.