This chapter emphasizes the importance of protein synthesis in determining what an organism is and what it becomes. Continuing to build the theme that organisms are genetic systems, the chapter focuses on Crick's Law, which states, for one, that nucleotide sequences determine amino acid sequences. Adding to the evolutionary theme of the book, the second part of Crick's Law, that the flow of information from genome to protein cannot be reversed, gives strong support for natural selection as the evolutionary mechanism, and leaves Lamarckian interpretations unsubstantiated. Another major theme, that organisms function through molecular interactions, is further illustrated by analysis of RNA synthesis, protein synthesis, and other processes involving interactions of large molecules in the cell. The last point of emphasis is that not all the organism's information for development and growth resides in its genome; some exists in the orientation of existing structures.