The chloroplast is the largest and arguably the most complex of the three energy organelles in the plant cell. The biogenesis of the chloroplast requires a combination of thousands of proteins encoded by the chloroplastic and nuclear genomes. Chloroplast function is also subject to modifications to enable responses to changes in environmental and developmental stimuli. As a consequence, interorganelle signalling and coordination between the chloroplast and nucleus is critical for the biogenesis and function of the chloroplast. Coordination and signalling during biogenesis is referred to as biogenic control and during the function as operational control (1). In this article, we report on two different mutant screens as examples of strategies for identifying mutations that affect biogenic and operational control signalling pathways and processes. We also describe strategies for the analysis and genotyping of the mutants.