Since the 1963 seminal review of Smith and French (62), our understanding of the chlorophyll (chl) biosynthetic pathway has changed dramatically. Several factors have contributed to this phenomenon, among which are: (i) development of systems capable of Chl and thylakoid membrane biosynthesis in organello and in vitro (17,28,42,43,46); (ii) development of powerful analytical techniques that allowed the qualitative and quantitative determination of various intermediates of the pathway (this chapter); and (iii) recognition of the probability that the structural and functional complexity of thylakoid includes a multibranched heterogeneous Chl biosynthetic pathway (44).