Living organisms exhibit various rhythmic phenomena, such as circadian rhythms, a heart beat, and breathing. Rhythmic phenomena in biology are driven by the dissipation of chemical energy and are generated in highly complicated nonlinear systems. To understand complexity in biology and in nature, studies of simple chemical models, which mimic the nonlinear dynamics of living organisms, are quite important. In the present article, we describe several chemical systems with nonlinear characteristics, such as spatio-temporal self-organization in coupled chemical oscillators, and chemical sensing based on the information in a time-dependent nonlinear response, which mimics the mechanisms of olfaction and taste sensation.