The paper analyses the beginnings of systematic ontology in Jainism, which appears to have began after first century CE, albeit certain ontology-relevant terminology in a nascent form was present earlier. A clear expression of systematic ontological reflection is the existence of models that organize ideas and categories in a more consistent conceptual scheme. Jainism follows similar developments that had earlier taken shape in in the early Buddhist Abhidharma, proto-Sāṁkhya-Yoga and proto-Nyāya-Vaiśeṣika. In addition, the paper argues that the models, five in (...) total, can be used as a methodological tool to distinguish various historical layers in early Jaina writings. (shrink)