Atmospheric turbulence is main limitation for ground-based optical observations. It reduces the resolution of ground telescopes and makes stars twinkling and boiling during observations. To overcome the limitation of atmospheric turbulence, many methods were proposed such as: adaptive optics, speckle interferometry and blind deconvolution. Before we discuss these methods, it is better to analyse the properties of atmospheric turbulence. (Added in 2014 Feb 28th.)