In the past decade, the medical effective dose per caput has increased in most European countries because of CT; it now ranges between 0.4 and 2 mSv/year. The biological impact of diagnostic imaging exposure is dominated by stochastic effects: based on the linear-no-threshold hypothesis, the risk of cancer induction is estimated to increase proportionally to organ dose, reaching around 0.5% at an effective dose of 100 mSv. The risk is higher the younger the age at the time of exposure, it is different for different organs, and women are more susceptible than men. Fluoroscopy-based imaging, above all intervention, may reach the dose threshold for deterministic effects, observed most often at the skin above around 3 Gy, and it is also the major source of occupational exposure in radiology. This white paper discusses the role of justification, evidence-based referral guidelines, optimization, diagnostic reference levels, clinical audits and quality assurance programs. The ESR strongly supports education and training of the medical staff involved in imaging by ionizing radiation. It disseminates information regarding radiation protection, takes initiatives, cooperates with partners and supports projects in justification as well as optimization. To reach these aims, the ESR cooperates with other organizations involved in radiation protection.