Etioplasts are plastids devoid of chlorophyll. They can be easily seen in the tissue showing scotomorphogenesis, i.e., plant development in the dark. When seedlings grow inside the soil in the dark, scotomorphogenesis takes place and photomorphogenesis is initiated as soon as they come out of the ground in light. Besides this, etioplasts are also found in light-grown-shaded tissues, and also form in dark periods of diurnal circadian rhythms. In monocot leaves, etioplasts can be seen at the leaf base, which is covered with the sheath. A developmental gradient of de-etiolation is created along the length of leaf with the oldest mature chloroplasts at the leaf tip and the younger plastid at the leaf base with the process of de-etiolation. Etioplasts contain lattice-like structures called prolamellar bodies, containing NADPH-POR-Pchlide complexes. These lattices are disintegrated in consonance with the conversion of Pchlide into Chlide upon receiving light and form thylakoids. There are numerous processes that influence this transition. Several biophysical, OMICs, physiological, molecular biology and genetics methods have been used to understand and characterize the process of de-etiolation. This chapter details these processes and captures new developments in the area of plastid de-etiolation. Also, how light affects miRNA expression, synthesis, processing, and function, as well as how it is involved in photomorphogenesis and de-etiolation/greening, will be discussed.