Dimethylgermylene (GeMe₂) has been generated and studied by 248 nm laser flash photolysis of 1,1-dimethyl- and 1,1,4-trimethyl-3-phenylgermacyclopent-3-ene (3a and 3b, respectively) in hexane solution, where it exhibits l_max = 470 nm and decays on the microsecond timescale with second order kinetics. In the absence of scavengers the decay of GeMe₂ is accompanied by the growth of absorptions due to tetramethyldigermene (Me₂Ge=GeMe₂; 2c, l_max = 370 nm), which then decays over the next ca 100 ms. Absolute rate constants for reaction of GeMe₂ with several reagents have been determined, including acetic acid, CCl₄, oxygen, n-butyl- and triethylamine, a terminal alkene and alkyne, two dienes, and the Group 14 trialkylmetallyl hydrides R₃MH (M = Si, Ge, Sn; R = Et or n-Bu). The rate constants agree closely with gas phase values for the same or similar substrates. The data are compared to those for reaction of GePh₂ with the same set of reagents, showing GeMe₂ to be significantly more reactive than its phenylated analogue in every case. The equilibrium constants for its reactions with the alkene and dienes, which are thought to yield the corresponding 3-membered germanocycles as primary products, are also considerably higher than those for reaction of GePh₂. Comparisons are also made with published data for SiMe₂ in solution. Absolute rate constants for reaction of digermene 2c have also been measured or assigned upper limits and are compared to those for the tetraphenyl analogue, providing the first quantitative assessment of the effects of substituents on the reactivity of the Ge=Ge bond.