There is high demand from the industry to produce high performance products with less manufacturing time and customised design of products. Additive manufacturing (AM) technique has the immense potentiality and is gaining ground in shaping the next-generation world. The various materials that have been developed so far using AM technique include SS 316, γ-TiAl, IN718, Ti–6Al–4 V, AlSi10Mg, high entropy alloys, etc. However, in order to facilitate rapid acceptability of this technique and to achieve the desired performance of the product, it is necessary to have highly isotropic microstructure with low defect density. It could be achieved only from the thorough understanding of the stochastic nature of defects formation and the complex non-equilibrium microstructure evolution mechanism via control over the processing parameters. Additive manufacturing (AM) technique is basically rapid solidification process and hence involves phase transformation under non-equilibrium condition. AM process has the impression of the complex multi-step thermal history on the evolving microstructure. Researches based on material, composition and processing parameters (hatch spacing, scan orientation, scan speed, laser power) are indeed necessary to create a processing-microstructure map for the additively manufactured material. The present chapter basically deals with the summary of researches on the microstructures that have been developed in various materials of engineering applications via different additive manufacturing technique and their effect on the mechanical property of the AM material. It discusses the manifestation of the microstructure evolution mechanism following the classical nucleation and growth phenomenon of the primary phase from the molten liquid and that of the secondary phase in the primary phase matrix within the melt pool boundaries and across them. It gives an overview of this novel technique with respect to its scientific and technical achievements and the scope to improve further.