Veterinary medicine is a major force for good, and ethics is a central, essential and unavoidable part of veterinary practice. We engage in ethical reasoning when we decide how to proceed in a clinical case, and by improving it we make better decisions for our patients, our clients and ourselves. Furthermore, it is a clinical skill that can be developed by experience, reflection, discussion and education. This article, the first in a series of three, aims to help practitioners engage in ethical reasoning and discussion. It does not (and should not) tell everyone what to do, but describes concepts and viewpoints that might provide the beginnings of a shared approach to veterinary ethical reasoning for cases faced in practice. It presents what appear to be shared values in the profession, their implications, unresolved questions and how debates might move forward. The second article in the series will apply these key principals to a specific case, and the third will present an approach to steps that can be taken in practice.