Inappropriate use of antimicrobials is perhaps one of the most threatening forms of wasteful clinical care. This is because inappropriate use of antimicrobials encourages the development of antimicrobial resistance (AMR). This chapter builds on available evidence to present a comprehensive set of policy actions to promote an effective use of antimicrobials. The chapter is divided into five sections. The first section analyses trends in consumption and estimates the share of inappropriate use of antimicrobials in OECD countries. This is followed by an assessment of the current and future health and economic burden caused by inappropriate use of antimicrobials and AMR. Section three spells out the main determinants underlying inappropriate antimicrobial use. Section four assesses the potential effectiveness of policy actions to promote an effective use of antimicrobials. Special emphasis is devoted to education and information activities; to organisational changes; and to a broader use of new technologies. A final section summarises the key policy implications of the chapter.