This chapter focuses on mechanical behavior under conditions of uniaxial tension during tensile testing. It begins with a discussion of properties determined from the stress-strain curve of a metal, namely, tensile strength, yield strength, measures of ductility, modulus of elasticity, and resilience. This is followed by a section describing the parameters determined from the true stress-true strain curve. The chapter then presents the mathematical expressions for the flow curve. The chapter reviews the effect of strain rate and temperature on the stress-strain curve and describes the instability in tensile deformation and stress distribution at the neck in the tensile specimen. It discusses the processes involved in ductility measurement and notch tensile test in tensile specimens. The parameter that is commonly used to characterize the anisotropy of sheet metal is covered. Finally, the chapter covers the characterization of fractures in tensile test specimens.