Eukaryogenesis was a foundational milestone in the origin of all complex life forms, including plants and mammals [1, 2, 3, 4, ∗∗5]. Eukaryotes are differentiated from bacteria and archaea by the presence of intracellular organelles such as the nucleus, mitochondria, and chloroplasts. The endosymbiotic theory posits that mitochondria and chloroplasts/plastids evolved from bacterial endosymbionts (i.e. symbionts inside the host cells) established within the host cell (Figure 1); in fact organelles are considered as one of the end points of endosymbiosis [6, 7, 8]. DNA sequencing of the mitochondrial and plastid genomes and biochemical studies have supported this hypothesis [9,10]. In addition, analyses of the organelle genome sequences have provided insights into the evolutionary outcomes of endosymbiosis [10,11]. Studies on naturally existing endosymbiotic systems have also provided de snapshots into the evolutionary transformation of a bacterium into an organelle [12,13]. In this review, we will focus on photosynthetic endosymbiotic systems and plastid evolution. We will first discuss some of the molecular signatures that serve as hallmarks of endosymbiotic evolution. Further, we will discuss the laboratory efforts to engineer cell-within-cell systems and artificial photosynthetic endosymbiosis between cyanobacteria and eukaryotic cells. We will also briefly discuss the lessons learned from these investigations as well as their implications on evolutionary biology and synthetic biology [5,14]. Particularly, we will outline how these platforms can serve as genetically tractable model systems to understand the evolutionary trajectories and molecular drivers of endosymbiosis and the transformation of photosynthetic endosymbionts into organelles.