The catalytic upgrading of vegetable oil to green diesel is one of the distinct research subjects in biorefineries. The catalytic conversion of triglycerides entails the method of hydrotreating such as hydrogenation, hydrodeoxygenation, decarboxylation and decarbonylation as well as isomerization. The product derived is renewable green diesel (straight chain hydrocarbon), of which its production addresses the sustainability of the future energy. The main challenges faced by hydrodeoxygenation are the selection and synthesis of suitable catalysts, selection of appropriate feedstocks, optimization of the thermodynamic parameters, and the reaction pathways. The literature on the selection of feedstock and model compounds is discussed in the sub-section. This review also includes the evaluation on several potential catalysts such as bimetallic solid acid, sulphided, non-sulphided, nitrides, phosphided, isomerization and hydrocracking catalysts as well as the noble metal catalysts. The selection of the metal supports catalysts, the catalyst designed practice and the overall performance is also reviewed and discussed. The most common supports used for the hydrodeoxygenation is solid acid composites such as Al2O3 and zeolites. In addition, the promoters tested yield different results with different reaction mechanisms demonstrated. The research on the hydrodeoxygenation pathways and the product distribution related with all kinds of catalysts are also addressed. In addition, the advancement of co-hydroprocessing of mix-vegetable oil and vacuumed gas oil is addressed and summarized as well. Overall, this review provides a comprehensive discussion on the hydrodeoxygenation issues and challenges in all relevant technical aspects. © 2017 Elsevier Ltd