Hypoxic regions have been identified within tumors and its presence has been linked to malignant progression, metastasis, resistance to therapy, and poor clinical outcomes following treatment. Acute and chronic hypoxia are integral components of tumor microenvironment and conduce to metabolic adaptations of tumor cells leading to genetic instability, intratumor heterogeneity and malignant progression. On the success of our fight against cancer, the continued adaptability of tumors to their microenvironmental stresses, such as hypoxia, must be considered. Tumor cells are endowed with a very high plasticity and capacity to adapt. It is our challenge to find populations and conditions of the tumor microenvironment germane for target success. Interdisciplinary work will be the key for achievement of these goals. This e-book is a compendium of original reports and review articles contributed by world-class experts in the field of tumor hypoxia. This material will be useful to foster discussion and increase understanding of the involvement of hypoxia in tumorigenesis, biomarker development, and therapeutics.Hypoxic regions have been identified within tumors and its presence has been linked to malignant progression, metastasis, resistance to therapy, and poor clinical outcomes following treatment. Acute and chronic hypoxia are integral components of tumor microenvironment and conduce to metabolic adaptations of tumor cells leading to genetic instability, intratumor heterogeneity and malignant progression. On the success of our fight against cancer, the continued adaptability of tumors to their microenvironmental stresses, such as hypoxia, must be considered. Tumor cells are endowed with a very high plasticity and capacity to adapt. It is our challenge to find populations and conditions of the tumor microenvironment germane for target success. Interdisciplinary work will be the key for achievement of these goals. This e-book is a compendium of original reports and review articles contributed by world-class experts in the field of tumor hypoxia. This material will be useful to foster discussion and increase understanding of the involvement of hypoxia in tumorigenesis, biomarker development, and therapeutics.