"If we are to use a criterion for choosing experiments to perform, the criterion of humanity is the best we could possibly invent. The greatest scientific experiments have always be the most humane."

- W. Russell and R. Burch: The Principles of Humane Experimental Technique, 1959

The 3Rs are the guiding principles for ethical practice in animal research. They stand for:

• Replacement: Replacement involves methods that avoid or replace the use of animal models. It can be further split into:
  • Absolute replacement: which for example includes the use of cell culture, organoids and organs-on-a-chip, as well as computer modeling of novel pharmacological compounds, and
  • Partial replacement: which involves the use of invertebrates, that show a lower level of pain perception such as Drosophila melanogaster - a common fruit fly - or even bacteria.
• Refinement: Refinement aims to improve animal welfare by reducing or avoiding pain, suffering and distress in animal experiments. This can be achieved by improving animal husbandry in research facilities, or by finding less stressfull procedures.
• Reduction: Reduction refers to methods that reduce the number of animals used per animal trial. The aim is to minimize the total number of animals while maximizing the gained knowledge per animal used at the same time.