Axion is one of the most compelling candidate particles for new physics beyond the Standard model. It is ubiquitous in a variety of well-motivated new physics scenarios and can address conundrums in the Standard Model, e.g., the strong CP problem. Indeed, research on axions is actively ongoing worldwide. In this talk, I will briefly overview axion physics and the current status of phenomenological research on axions. If I have enough time, I will introduce my recent work on ‘Axion magnetic resonance’.