Mostly in Prakrit—especially Ardhamāgadhī. Early Jain canon (the Āgamas, per the Śvetāmbara tradition) is in Ardhamāgadhī; some early material also appears in Śaurasenī/Māhārāṣṭrī. Later, many Jain works (like Tattvārtha Sūtra) were composed in Sanskrit.