Mean flow measurements and short-duration Schlieren and Shadowgraph photographs of heated and unheated supersonic slot injection of air into a supersonic air stream are presented for the purpose of observing the mixing which occurs in the resulting shear layer. The heated injected jet (M_j, P_tj = 10.7 psia, and T_tj = 760°R) passes through a slot of height 0.475 inches (1.2 cm) tangent to a free stream with M_∞ = 3.0, P_∞= 95 psia and T_t_∞ = 540°R. The resulting density ratio is P_j / P_∞ = 0.3. The free stream Re/ft = 6.1 x 10⁷ (Re/cm = 2 x 10⁶). The thickness of the plate which separates the primary and secondary flows is 0.021 inches (0.052 cm). Pitot pressure, cone static pressure and stagnation temperature profiles are obtained at four axial stations downstream of the slot (x/H = 0.25, 4, 10, 20). An additional set of measurements is obtained at Station 4 for the case of a weak shock (P₂/P₁ = 1.8) interacting with the shear layer just upstream of Station 4. From the pressure and temperature measurements, Mach number, velocity, density, mass flux and static pressure profiles are generated. An unheated injection study is also performed at the same flow conditions for comparison to the heated case. The heated and unheated cases are very similar except in the slot where the temperature difference creates changes inp, U, and pU. This study is thus concerned with the effects of changes in P_j / P_∞ and U_j / U_∞, especially (U_j - U_∞), which are created by heating the injected flow. The heated slot flow did not create a marked difference in the location of the merging of the free stream boundary layer with the slot flow when compared to the unheated slot flow. Indeed, the appearance of the two flows on Schlieren photographs is similar even though the injected mass flow in the heated case is about 15% less than that in the unheated case. The pressure adjustments in the slot lip region are different for the two different cases. The flowfields are documented for both the heated and unheated cases with the added measurements and photographs for the shock impingement case. / Master of Science