A lecture given by Saurabh Kundu, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. Theory for the selection of specific crystallographic variants out of all possible variant, when steel is transformed into bainite, martensite or in general, displacive phase transformation products. Variant selection during displacive transformation is popularly monitored by assessing the pole figure or ODF of the bulk texture or pole figures from single prior austenite grains and also by measuring the physical orientation of alpha' plates in the microstructure. However it is known that when variant selection occurs the shear strain associated with each alpha' plate does not get fully cancelled and it is reflected in the measured transformation strain. We have shown in this work that transformation strain is the most reliable measure for the variant selection. Mathematical models have already been developed to calculate the transformation strain under various loading conditions, and to support the same extensive experiments have been done to show how externally applied stress and plastic strain can affect the transformation strain. This data is used to describe the extent of variant selection which is further supported by EBSD results. Interesting observations has also been made on the nature of the strain during transformation. Finally mathematical models have been developed to show that variant selection has negligible influence on physical orientation of alpha' plates when transformation occurs under external stress only, but prior plastic deformation can change the orientation to a great extent.