Chapter 6 examines the legal concept of evidence and the key dimensions of relevance, strength and reliability. I argue that a purely probabilistic conception of evidence is insufficient and present a causal perspective on evidence. The causal approach provides a unified framework to capture the interrelations between hypotheses and evidence and helps us to assess probabilistic relevance and strength. This perspective lays the foundation for a principled approach to modelling legal cases, which I develop in Chapter 10.