In this article, we describe the instability of a contact line under
nonequilibrium conditions mainly based on the results of our recent studies.
Two experimental examples are presented: the self-propelled motion of a liquid
droplet and spontaneous dynamic pattern formation. For the self-propelled
motion of a droplet, we introduce an experiment in which a droplet of aniline
sitting on an aqueous layer moves spontaneously at an air-water interface. The
spontaneous symmetry breaking of Marangoni-driven spreading causes regular
motion. In a circular Petri dish, the droplet exhibits either beeline motion or
circular motion. On the other hand, we show the emergence of a dynamic
labyrinthine pattern caused by dewetting of a metastable thin film from the
air-water interface. The contact line between the organic phase and aqueous
phase forms a unique spatio-temporal pattern characterized as a dynamic
labyrinthine. Motion of the contact line is controlled by diffusion processes.
We propose a theoretical model to interpret essential aspects of the observed
dynamic behavior
