Layered materials are solids consisting of crystalline sheets with b in-plane covalent bonds and weak van der Waals out-of-plane interactions. These materials can be easily exfoliated to a single layer (1L), obtaining two-dimensional (2D) materials with radically novel physico-chemical characteristics compared to their bulk counterparts. The field of 2D materials began with graphene and quickly expanded to include semiconducting transition metal dichalcogenides (TMDs). 2D materials exhibit very b light-matter interaction and exceptionally intense nonlinear optical response, enabling a variety of novel applications in optoelectronics and photonics. This talk will review our studies on the non-equilibrium and nonlinear optical response of 2D materials. We will discuss ultrafast carrier and spin dynamics in 2D semiconductors and their heterostructures. We will also show gate-tunable absorption saturation and third-harmonic generation in 1L-graphene and optical parametric amplification in 1L-TMDs.