A theory for crack formation in reinforced concrete elements based on an analysis of slip, bond stresses, and steel stresses is presented. The problem is treated as an initial value problem both for initial crack formation when the cracks are independent, and for stabilized crack formation when the zones of bond stresses reach each other. Simple rules for analysis are presented for initial crack formation derived from the analytical solution of the mathematical model using homogeneous initial values. As an application, the spalling crack width control of a prestresesd pretensioned bridge girder is estimated. Numerical analysis is presented for stabilized crack formation. Tension stiffening is analyzed as a result of the interface behavior.