This chapter turns to medical interventions, preventive, therapeutic and palliative interventions, as well as their effectiveness and efficacy, to the role of placebos and nocebos in clinical trials and in clinical medicine, to evidence-based medicine, to cancer screening and to the paradox of health education. Treatment is a medical intervention intended to be beneficial, or to do more good than harm. A medical intervention ideally aims to reach some ultimate objectives such as to eradicate or cure a disease; slow its progression; relieve its suffering and other symptoms; prevent illness or injury, recurrence, complications, comorbidity, or premature death; limit disability and reduce communicability; restore functional capacity and care for those who cannot be cured. A treatment is an intended medical intervention and there is good inductive evidence that the treatment is linked with the expected improvement by a causal chain. Most treatments have unintended effects and many of those are undesirable and constitute a spectrum of side and adverse effects besides their positive remedial effects. Adverse effects raise the issue of comparative risks: in the presence of two equally efficacious treatments we shall choose one of them on account of its less severe and less frequent overt side effects. Patients may improve or survive in spite of medical interventions rather than because of them. Compliance (also adherence, capacitance) describes the degree to which a patient correctly follows medical advice. Noncompliance is the bane of clinical medicine and medical investigations. It allows dying with comfort or dignity. A Placebo is a non-efficacious intervention that is used in RCT’s. It is also a non-efficacious intervention that may be used deliberately and as a standard-in for treatment, or unwillingly be either self-administered or administered by the health team. Evidence-based medicine (EBM) integrates clinical experience and patient’s values with the best available research information.