Answer

There is no single universally accepted “definitive book of Jainism” for all Jain traditions.

However, the most foundational Jain scriptures are the Āgamas — the canonical teachings preserved especially in the Śvetāmbara Jain tradition.

Explanation

In Jain Dharma, authority is not based on one book alone. Jain teachings come from the enlightened knowledge of the Tīrthankaras, especially Bhagavān Mahāvīra, and were preserved through the Jain scriptural tradition.

Important categories include:

• Āgamas – canonical scriptures in the Śvetāmbara tradition.
• Tattvārtha Sūtra – a highly respected philosophical text accepted by both Śvetāmbara and Digambara traditions, though with some differences in interpretation.
• Samayasāra – an important Digambara text by Ācārya Kundakunda focusing on the nature of the soul.
• Uttarādhyayana Sūtra – a well-known scripture containing teachings on conduct, renunciation, karma, and spiritual discipline.

Spiritual Understanding

Jainism is a path of right faith, right knowledge, and right conduct. Scriptures guide the soul toward understanding:

• ahiṃsā — non-violence
• anekāntavāda — many-sided truth
• aparigraha — non-possessiveness
• karma theory
• liberation of the soul

Takeaway

If you want one starting text, Tattvārtha Sūtra is often considered the closest to a concise, systematic overview of Jain philosophy across major Jain traditions.