This review aims to understand everyday learning of older adults using mobile devices. Specifically, for both academic and practical implications, we wanted to know what theoretical perspectives researchers adopted and how mobile devices play a role in older adults' informal learning. We analyzed 28 empirical studies (15 qualitative, 10 quantitative, and 3 mixed methods) that met our selection criteria. Our findings revealed that the studies used four theoretical frameworks to understand their learning: (a) technology acceptance theory, (b) experiential learning theory, (c) social cognitive theory, and (d) activity theory. We also identified six themes of older adults' informal learning using mobile devices through key findings from the existing studies: (a) self-learning of health or medical knowledge, (b) affective and emotional dimensions, (c) ambivalent attitudes, (d) practical uses, (e) interpersonal and intergenerational communication, and (f) collaborative learning experience. We conclude this article with discussion for research and practice.