The potential importance of RNA stability to the regulation of chloroplast gene expression is documented by recent work on the molecular aspects of chloroplast biogenesis. In Chlamydomonas reinhardtii, two lines of evidence support the idea that gene-specific regulated RNA decay plays a crucial role in determining the different steady-state levels of single transcripts. First, during the cell cycle, a light-dependent and/or circadian control of RNA accumulation takes place that appears to involve both transcriptional and posttranscriptional mechanisms. Secondly, numerous well-characterized photosynthetic nuclear mutants exhibit defects in the stabilization of specific Chloroplast transcripts. This further substantiates the significance of gene-specific aspects of chloroplast RNA metabolism.