This lecture covers the relationship between crack growth conditions and the energy release rate, defined as the Strain Energy Release Rate G. It explains the stress field ahead of a crack, stress intensity factors, and the effect of cracks on modulus. The instructor introduces the concept of crack-tip energy dissipation and the generalization for ductile materials. The lecture also discusses small-scale yielding and the 'process zone' near the crack tip where all dissipative processes occur.