An outstanding problem in the field of complex dynamical systems is to control non-linear dynamics on complex networks. Indeed, the physical world in which we live is non-linear, and complex networks are ubiquitous in a variety of natural, social, economical, and man-made systems. Dynamical processes on complex networks are thus expected to be generically non-linear. While the ultimate goal to study complex systems is to control them, the coupling between non-linear dynamics and complex network structures presents tremendous challenges to our ability to formulate effective control methodologies. In spite of the rapid development of network science and engineering toward understanding, analyzing and predicting the dynamics of large complex network systems in the past 15 years, the problem of controlling non-linear dynamical networks remains to be outstanding.