The behavior of biological systems may change discontinuously in response to continuous changes in the environment or external signals. In this chapter, we will understand this phenomenon as bifurcation behavior in the dynamics of biological systems. The importance of bifurcation in biological functions and their understanding is gradually increasing. This chapter is also closely related to the regulation of chemical reaction systems studied in the previous chapter. In Chap. 8 , it was shown that the response range of a chemical reaction system to an enzymatic change is determined by the “buffering structure.” In this chapter, we show that buffering structures govern not only enzymatic regulation but also another important aspect: bifurcation.