Ultrafast Two-Dimensional Electronic Spectroscopy (2DES) has emerged as a powerful tool to probe excited-state dynamics in photosynthesis, photovoltaic materials, quantum dots, and two-dimensional materials in recent years. Compared to one-dimensional time-resolved spectroscopy, 2DES not only contains one additional dimension to resolve excited-state dynamics but also provides rich information about homogeneous and inhomogeneous broadening, intermolecular coupling and coherent dynamics that are not fully accessible to the traditional third-order spectroscopic methods. Here we will briefly introduce the principle of 2DES from the basic concepts such as Fourier-transform linear spectroscopy, and transient grating. Subsequently, we will illustrate the applications of 2DES in the context of recent studies of spectral broadening in two-dimensional materials, and charge separation and coherent dynamics in photosynthesis and photovoltaic materials. Finally, we will discuss the remaining challenges and exciting future directions for the fields of 2DES.