单晶是指其内部微粒有规律地排列在一个空间格子内的晶体。其晶体结构是连续的，或者可以说，在宏观尺度范围内单晶不包含晶界。

与单晶相对的，是众多微晶（Crystallite）组成的多晶（Polycrystal）。

单晶材料是一种应用日益广泛的新材料，由单独的一个晶体组成，其衍射花样为规则的点阵。相对普通的多晶体材料性能特殊，一般采用提拉法制备。

单晶根据晶体生长法制作分为：

A single crystal or monocrystalline solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. The absence of the defects associated with grain boundaries can give monocrystals unique properties, particularly mechanical, optical and electrical, which can also be anisotropic, depending on the type of crystallographic structure. These properties, in addition to making them precious in some gems, are industrially used in technological applications, especially in optics and electronics.