Zoyaku (Zoeki) is the term for the taxation system introduced after the middle of the Heian period.
Whereas Kanmotsu (tribute goods paid as taxes or tithes) and Nengu (land tax) are considered as the transformation of the tax, So (rice tax) of the Ritsuryo system (a system of centralized government based on the ritsuryo code), Zoyaku indicated Zokuji (all miscellaneous dues in the form of non-rice products and labor), Buyaku (labor service), Rinji Zoyaku (extraordinary irregular levies) that are considered as a continuance of a per-capita tax, Zoyo (irregular corvee) (regarding what the taxes of Yo [labor or alternative goods] and Cho [textile goods or alternative money] transformed into, there are two theories: one theory asserts Kanmotsu and another Zoyaku). There were koden (field administered directly by a ruler) and shoen (manor in medieval Japan) that applied to the Kokushi in advance to be exempt from Zoyaku. This was called Zoyakumen (exemption of Zoyaku). Originally it was a tax on prominent citizens, but with the establishment of Kanmotsu rippo (the law fixing the tax rate of kanmotsu, tribute) in the middle of the 11h century, it transformed into a tax against land.