Studies using the unicellular green alga Chlamydomonas reinhardtii have earned a role in building our understanding of photosynthesis and chloroplast biogenesis through a combination of fortuitous natural characteristics and hard work by many investigators. The most critical contributor to this role is the development of tools for genetic and molecular genetic analysis. Photosynthetic processes span a wide range of temporally and mechanistically distinct phenomena that are intertwined with one another in ways that are both subtle and profound. Many of the biophysical, biochemical and physiologic techniques that can be exploited for investigating photosynthesis operate within restricted ranges of this temporal domain. Genetic analysis is an investigative approach that extends across these domains and provides a basis for integrating the understanding that arises from many other types of studies. Studies exploiting the favorable characteristics of C. reinhardlii are continuing to prove their worth in the forefront areas of structure-function analysis of photosynthetic complexes, metabolic regulation and coordination of photosynthesis, and regulation of chloroplast biogenesis. Although they have already been uniquely valuable in the past, the range and precision of the tools for genetic analysis in this alga are currently being improved rapidly and dramatically. Research in photosynthesis will be a significant beneficiary.