AbstractThis chapter examines preposition incorporation (P-incorporation) in Older Icelandic, i.e. leftward movement of a preposition which adjoins to the left of a main verb or participle. As expected, P-incorporation in Older Icelandic obeys the Head Movement Constraint (HMC) and the Adjunct Condition, whether the [P+V/Part] complex forms a morphological word or not. In the latter case, excorporation from the [P+V/Part] complex is possible. P-incorporation requires the presence of a bare PP complement but this option was lost in the 19th century when, according to our hypothesis, the presence of the categorizing head p became obligatory in all PPs. P-incorporation became impossible as a result as it would inevitably violate the HMC or improper movement. Finally, it is shown that P-incorporation cannot take place from an OV-structure, a restriction that can be derived if OV-orders require leftward movement of the verbal complement.