This thesis is primarily concerned with the developments that have taken place in infinitival constructions in the late Old English, Middle English, and Modern English periods. It is an investigation into the status of Old English to-infinitive, the origin, nature, and distribution offor in Middle English (for)to-infinitival constructions, and the origin and reanalysis offor as a complementiser in the Modern English [for DP to VP] construction. In chapter one, we introduce some of the basic notions of the Minimalist Program outlined in Chornsky (1993,1995)). The airn of chapter two is to account for the structural status of to in the Old English toinfmitive. It is argued in this chapter that firstly (functional) C, Agr, and T are not eligible positions for to, and secondly that to occupies the lexical category P(reposition). The prepositional status of the Old English to-infinitive is supported by the fact that it occurs in coordination with ordinary PPs. Chapter three argues that the Old English to-infinitive should be treated as a single (morphological and) syntactic unit which cannot be broken up by intervening elements. We propose that to is generated with a D-feature and that the infinitival verb is a combination of two features: an Inf-feature and a D-feature. We argue that as long as V+W-to-D movement is attested, the syntactic unity cannot be broken up by elements like objects, adverbs, etc. Once the Old English case system disintegrated, the internal structure of the to-infinitive underwent a radical change such that the demise of -ne (which resulted from the weakening of to as a dative case-assigneri resulted in the demise of D, and this led to the disintegration of the syntactic unity of the to-infinitive, and the consequent appearance of for before to. In other words, when to ceased to be a preposition, for moved in and 'took over' (and perhaps became an infinitival marker as well, givingforto). In chapter four, we proceed to account for the structural status offor in Middle English to-infinitive. Three analyses that attempt to account for the status of for are examined and rebutted in favour of our analysis of for as part of the infinitival morphology. Chapter five provides morphological and syntactic evidence in favour of analysingfor and to as a compound infinitival marker. It is argued that the position of the compound infinitival marker (for)to is T(ense). This analysis correctly predicts (for)to to be present in raising and control infinitives. A number of factors which show that (for)to occupies T will be noted and discussed. The purpose of chapter six is to provide evidence for the correlation between verb movement and object shift in Middle English (for)to-infinitives. It will be argued that the infinitival verb moves overtly from VP to Inf, the functional head which hosts the infinitival feature. Some empirical evidence relating to conjoined structures and VPadverbs is discussed. The attestation of V-to-Inf movement in Middle English (for)toinfinitives is strongly supported by the presence of object shift. Our conclusion is that the non-attestation of object shift in Modern English to-infinitives can be attributed to the absence of overt V-to-Inf movement. Having established the morphological and syntactic status of the infinitival marker (forfto (chapter five) and the infinitival verb (chapter six), we proceed to investigate the origin offor in the Modem English [for DP to VPJ construction. On the basis of morphological and structural evidence, we propose that the [for DP to VP] construction is the outcome of two diachronic reanalyses (DRs), which took place at two different stages in the history of English. The first DR, which took place in the 12th century, was triggered by the loss of dative case which paved the way for the introduction of prepositions like for to realise the benefactive function. In Old English the benefactive function was typically associated with morphological dative case. Once dative case had been lost, the beriefactive. function had to be realised by prepositions likefor. Throughout the Middle English periodfor was a case-realiser and not a lexical preposition. Its main function was to realise an inherent case feature which belonged to the matrix lexical head. The second DR, which occurred in the 16th century, was triggered by the fact that the string [for DP to VP] had become structurally ambiguous for acquirers, allowing an interpretation where [for DPI is part of the matrix predicate, or alternatively an interpretation where [for DPI is the subject of the infinitival clause. In the latter interpretation for's function is to realise a Case which does not belong to any lexical head. It realises the Case property of the C-position. It will be argued that the prepositionfor was reanalysed as a complementiser as a result of the loss of infinitival clauses as complements of prepositions, and the consequent development of the C-position as a potential accusative Case licenser. The change can be regarded as a change in the status offor from a lexical case-realiser to a functional Case-realiser.