This chapter, the first of the two empirical chapters, analyses the definitions, contributing sciences and core values of One Health approaches such as One Health, EcoHealth, Planetary Health, and One Welfare. These four have been chosen as the main ones among others. Both meta-ethical and ethical aspects found in core texts of the different approaches are summarized here. Meta-ethical aspects address issues such as views on moral status, how to include ethics in the approach, and what kind of values should be considered. Ethical aspects cover core concepts that a sufficient ethical framework for One Health approaches need to be considered. The grid in One Health approaches is broad. One has both to consider different levels (individual, population, and ecosystem) as well as species (at least humans, animals, and plants).