Fruit, as an evolutionary innovation, helps to protect and disperse seeds in angiosperms. To fulfill such functions, fruit forms have diversified to display numerous types and morphologies, including a diversity of shapes and sizes, and even novel forms. Developmental genetics has revealed how fruit organs initiate, how fruit forms develop, and how they have evolved. Here, we summarize the accumulated knowledge of the genetic basis underlying these developmental and evolutionary processes in model plants, such as Arabidopsis, rice, and tomato. The molecular basis underlying carpel organ identity and functionality seems to be evolutionarily conserved. In contrast, the developmental trajectories in post-initiation processes are too diverse to generalize a developmental genetic toolkit or propose a theoretical, unifying model for fruit formation that explains the transition of fruit types and morphogenesis. Developmental repatterning is considered to play a role in fruit diversification, which could be primarily accomplished through variation in gene expression over time, space, and/or dosage, thereby generating diverse morphologies. A comparison between closely related species to show developmental and genetic variation during fruit development is the key to addressing the mechanisms underlying developmental repatterning. The current knowledge on fruit patterning and repatterning from model plants is expansive. However, additional models are critically needed to better understand these general processes. Lastly, we argue that an evolutionary development biology (evo-devo) perspective could provide a multi-dimensional view to understand how fruits form and repattern, why fruits evolve, and further provide insights into crop design and breeding.