The role of land agents in the management and improvement of English landed estates between 1770 and 1850 is examined in this paper. The focus is on the responsibilities of land agents, their contribution to agricultural improvement, and in particular the validity of a thesis of the professionalisation of agents during this period. The Petworth House archives are used to compare the work of two legal agents at Petworth in Sussex with that of a professional land agency firm in Yorkshire, both employed by the third Earl of Egremont (1751–1837). This study suggests that the role of land agents in agricultural improvement at Petworth was limited to the financial, legal and political aspects of these developments rather than practical management. It proposes that legal agents remained more influential than has been supposed, even on estates renowned for agricultural improvement, and despite contemporary criticism that emphasised the importance of applied agricultural expertise. The belated professionalisation of the Petworth agents and the significant differences in their roles when compared with contemporary and historical accounts suggests that estate management was therefore far more diverse than is suggested in some recent literature.