1 Introduction: 1.1 Introduction; 1.2 Some completed trials; 1.3 Choice of design; 1.4 Practical constraints; 1.5 Influencing clinical practice; 1.6 History; 1.7 How trials arise; 1.8 Ethical considerations; 1.9 Regulatory requirements; 1.10 Focus; 1.11 Further reading. -- 2 Des…