「什麼是課程？」，這個課程領域的永恆問題，是影響課程領域造型與賡續發展最為關鍵也最為基礎的問題。本文旨在通過回顧美國課程研究中再概念化學派(reconceptualists)發展的歷史轉折，重新探究課程本質，以澄清課程的根本內涵。本文首先透過對課程再概念化學派的歷史回顧，重新闡述其主張與自我定位；繼之通過Helbowitsh一九九九年針對課程所牽涉到的課程實踐問題、課程設計問題以及課程領域處境與歷史承繼等問題，對再概念化學派的一系列詰問，試圖梳理出再概念化學派對課程本質的理解主張，以深入理解再概念化學派對課程的允諾與所做定義。本文以再概念化學派所引發的爭論為線索，希望對課程本質重新加以釐清，並指出未來課程研究的發展方向。

The eternal question about what curriculum is could be the most significant and fundamental one in the curriculum field, because it affects the shape and subsequent development of curriculum. This paper aimed at clarifying the definitions of curriculum by re-exploring the nature of curriculum, through a review of the historical development of the Reconceptualists in the American curriculum studies. First of all, this paper tried to explicate the Reconceptualists' claim and self-orientation by means of a historical review. In order to exhibit the Reconceptualists' commitments and their definitions of curriculum, an elaboration on the Reconceptualists' position regarding the nature of curriculum was then followed, through a presentation of a series of questions posed by Helbowitsh in 1999 concerning the issues involving curriculum practice, curriculum design, the situation of curriculum field and its historical heritage, and Pinar's response. Not only did this paper investigate the transition of the curriculum definitions by looking into the transfiguration of the Reconceptualists, it also tried to offer a historical evaluation of the Reconceptualists through such a review of its changing process. It hopes to further explicate the nature of curriculum with reference to these related debates in order to provide some directions for the future curriculum understanding.