The new institutional economics has emphasized the importance of ideology in determining the content and direction of institutional change. Ideology can also determine when interest groups succeed in achieving legislative favor. The case of the regulation of in-kind wages in Britain shows that factors highlighted in mainstream political economy (such as interest group strength and organization, self-interest of legislators, and coalitional partners) were important. However, the interaction between relative price changes and social ideology was also significant in explaining the shape and timing of legislative changes. Changes in relative prices gave labor groups the incentive to seek legal protection from non-monetary wages, but they obtained protection only if they met certain criteria established by the prevailing ideology. Changes to that ideology resulted in further legislative changes granting cash wages to most industrial workers.