This chapter discusses the interesting topic of flame dynamics. The chapter starts by presenting the flame as a discontinuity, introducing the vector equations of the flame surface, the definitions of the normal unity vector, the normal flame propagation velocity, and the relative flame speed. These definitions are given in detailed form. It should be pointed out that these definitions are related to lectures on fluid dynamics. Afterwards, the concept of flame deformation, or stretch, was introduced. The flame stretch theory is presented by deriving the stretch rate equation and analyzing the effect of flame stretch on the flame speed and temperature. The dimensionless numbers of Karlovic and Markstein are introduced together with the Markstein length, which is important to fundamental experiments on laminar flame velocity. Afterwards, the chapter presents some theoretical and experimental aspects of a flame propagating inside a closed (or half-open) duct (or tube). Finally, the chapter is closed by introducing the dimensionless form of the governing equations.