Graphene as a 2D carbon nanostructure has drawn tremendous interest worldwide because of its extremely high mobility and unique electronic, magnetic, and surface properties but opening a band gap remains challenging. Other 2D materials have emerged as promising materials that may be more easily altered to have a band gap, high mobility, and on/off ratio. Germanene with its buckled two-dimensional structure exhibits extremely high mobility, massless fermions behavior, and strong spin-orbit coupling which has drawn tremendous interest for high performance devices. However, it has no intrinsic band gap and low structural stability which are needed for logic and switching devices. Despite numerous attractive features in germanene it, like graphene, exhibits a semi-metallic zero band gap. Applying electric field, chemisorption of adatom species, introducing periodic nanoholes, doping and edge functionalization are all techniques aimed at opening a bandgap in germanene. Here we present a density functional theory based study of the influence of edge-functionalization using hydrogen (-H and -2H) and halogen (- F, -Cl, -Br, -I, -2F,-2Cl, -2Br, -2I), -S atoms and –SH, -OH, -CH₃ groups termination. An overview is given of the influence of these edge-functional groups attached to different germanene nanoribbon (GNR) structures of varying width ranging from 6 to 19, focusing primarily on band gap. Additionally, the dependence of armchair GNR band gap on functionalization and ribbon width is explored. We found that edge functionalized armchair germanene nanoribbon (AGeNR) opened a band gap as small as 0.012 eV when functionalized by -2H and could be as high as 0.84 eV when functionalized with -2I. Nanoribbons could be classified into three families according to width as follows, W = 3K, 3K+1, and 3K+2. For mono-hydrogenated, fluorinated, chlorinated, hydroxyl termination, the band gap varied as E_G (3K+2) < E_G (3K) < E_G (3K+1).  For di-hydrogenated, fluorinated, and chlorinated we found band gap follwed the periodicity E_G (3K+ 1) < E_G (3K +2) < E_G (3K ). Formation energy studies revealed that the AGeNR produced a more stable structure with fluorine functionalization and -SH, -OH, -CH₃ group’s termination also provides similar result with sizable band gaps. Simulation results suggest that the electronic structure of germanene is similar to graphene and silicene. Energy band gap tuning of AGeNR using edge functionalization may provide a new means of integrating germanene in optoelectronics, low power and high performance switching devices.