Summary In the County of Holland, in the sixteenth and seventeenth centuries the rules regarding security interests in movables changed fundamentally. Rules of doctrine came to be combined with rules found in local law, that is the bylaws of cities and regions. This went together with the re-interpreting of fragments of older bylaws. In 1631 Grotius’ Inleidinghe categorized the lien of the unpaid seller after delivery of the merchandise sold as entailing a reivindicatio . This new rule was adopted in cities in Holland, even though it ran counter the earlier approach that third-party effects of sales in this regard were very limited. Also, the new line of thought that holders with a legitimate title did not respond to pledgees pushed out older conceptions on tracing for some special pledges. In their legal writings Dutch authors after Grotius attempted to construe consistent solutions; in the legislative practice of cities, older rules could be preferred over new ones. Bylaws of cities, to which authors of Roman-Dutch doctrine referred as well, stipulated limits on tracing by unpaid sellers. All the mentioned developments were not determined by changes in the market, even though they could be incited by them. Legal change in Holland, even in the Golden Age of the seventeenth century, was due more to the embracing of academic ideas than to responsiveness to economic conditions.