The last decade has witnessed an exponential interest in land investments across numerous industries in the developed countries. Africa has been particularly targeted for investments, increasingly for biofuel production. Though land investments can boost local economies when realized in an equitable manner, many reports also point to large-scale displacements and loss of land for local landowners. There remain empirical unclarities on the subject, and theoretical and analytical frameworks are underdeveloped in explaining the conditions and factors that determine outcomes.   This thesis is exploring the effects of land investments on land tenure security through the lens of credible commitment and neo-patrimonial theory, with a focus on biofuel production in Tanzania as the chosen qualitative case study. The analysis is based on two specific jatropha investments in Tanzania: Sun Biofuels and Diligent Ltd.   The research contribution of the thesis is in merging two theoretical approaches, CCT and Neo-patrimonialism, and applying it to a new research area of land investments in order to establish an understanding of their effects on local land tenure security.