This paper provides novel documentation and description of the verbal modal system in Great Lakes Bantu languages. Runyambo (E21/JE21) is compared with Luguru (G35). The paper builds on Bostoen et al. (2012) and Kawalya et al. (2014, 2018) to revisit Runyambo data and add data from Luguru to reexamine findings in the Great Lakes Bantu Languages. This study is the first to discuss necessity modality in Rutara languages and the very first description of modality in Luguru. The study was conducted in Karagwe and Kyerwa Districts of Kagera Region and Morogoro Rural and Mvomero Districts in Morogoro Region. The field work that involved 10 informants included collection of written texts and in-depth dialogues and interviews for collecting oral texts. The study presents the modal baas- ‘be able’ as the only modal verb for expressing possibility in Runyambo language. Moreover, the modal baas- in Runyambo as opposed to dah- ‘be able/capable/permitted’ in Luguru, has both modal and lexical functions. We demonstrate further that the modal verb teekw- ‘must/ought to’ is used to express both weak and strong necessity in Runyambo. The modal teekw- modifies all verb types and it requires the auxiliary verb to either refer to the past or future. The modal verbs dah- ‘beble/capable/permitted’ and bamigw- ‘must/ought to’ in Luguru express possibility and necessity respectively. It is fascinating to identify that in both languages the modal verb for necessity requires both progressive formative and subjunctive form of the immediate verb. Lastly, we demonstrate that in the two languages the modal verbs interact with different tense and aspect formatives.