契約準據法應否依「當事人意思自主原則」選擇準據法之問題，一直存有否定論與肯定論之爭，雖「當事人意思自主原則」否定論之論據並非無理，但「當事人意思自主原則」肯定論乃是長期具體存在之實證法，故堅持否定論，不免昧於現實，且對「當事人意思自主原則」具體運用上所生問題之解決無所助益。故現階段應思考者，係究應以何種方式適當地、合理地限制「當事人意思自主原則」於契約之適用以防止其被濫用，亦即於現行之國際私法制度下，應如何劃定「當事人意思自主原則」運用於契約之一合理界線。就現階段國際私法觀察，可運用於管制「當事人意思自主原則」之制度工具，有「規避法律」、「公序」、「即刻適用法」、「第三國強行債法連繫」、「跨國公序」、「質的限制」、「量的限制」等七項，故而本文乃就此七項可運用於管制「當事人意思自主原則」之制度工具加以分析評估，並探討此七項制度工具如何維護契約衝突法之「衝突正義」與契約實體法之「契約正義」，以得出「當事人意思自主原則」運用於契約之一合理界線。

It is no doubt that ”party autonomy” is one of the most important rules on conflicts law. But there are still some advocates of the objection of ”party autonomy”. Although the objection of ”party autonomy” is not groundless, ”party autonomy” is positive law in the real world. Therefore, it is more significant to line a reasonable boundary line of ”party autonomy” than to object it. In contemporary conflicts law, there are seven techniques to regulate ”party autonomy”, including ”fraude à la loi”, ”ordre public”, ”connected be the mandatory obligation law of a third country”, ”lois d'application immediate”, ”transnational public policy”, ”limited by quality” , and ”limited by quantity”. This article will evaluate how these techniques maintain the conflicts justice of conflicts of contract laws and the justice of contract law and also conclude a reasonable boundary line of ”party autonomy” to apply in conflicts of contract laws.