Latin influenced the development of Old English more than any other non-West Germanic language with which Old English came into contact. Most scholars divide the influence of Latin chronologically into three time periods. The first time period concerns such influence as occurred on the continent prior to the arrival of Anglo-Saxons in England and which arose from contacts between West-Germanic speaking peoples and Latin speakers. The second period of influence spans from the arrival of the Anglo-Saxons in England up to their Christianization ca. 600/650. The last period of influence spans from the time of Christianization up to the arrival of the Normans in 1066.
The most readily apparent influence that Latin had on Old English concerns the use of the Latin alphabet. Prior to the Christianization of England, what little writing there was, there was written with runic letters. Collectively these letters comprised the futharc alphabet (called so after its first six letters). Through the influence of Irish insular script, Old English scribes adopted the Latin alphabet. They did so with only slight modification and the retention of certain runic letters. Modifications included the use of Latin with a line through it, <ð> ("eth"), to represent both /q / and /ð/. Somewhat later, they also used the rune thorn, <þ>, to represent these two phonemes. Finally, they incorporated the rune wynn, < >, to represent /w/.
It is more difficult to determine Latin influence on Old English syntax. Naturally, our knowledge of Old Englis syntax is hindered by the general paucity of extant Old Englih texts. Furthermore, many of the surviving Old English texts are translations of Latin texts, and even when they are not, many nonetheless reflect a clear dependence on Latin models. Consequently, it is difficult to account for the syntactical irregularities of Old English texts with any certainty. Such irregularities could represent the influence of Latin or – just as likely – an otherwise poorly evidenced aspect of Old English syntax. Nonetheless, scholars agree that certain constructions – whether native to Old English or not - likely did find wider distribution in Old English through the influence of Latin than would otherwise have occurred. Such was likely the case, for example, with the Old English "dative absolute" construction as modelled on the Latin "ablative absolute." While this construction appears rarely in the conservative prose of the Anglo-Saxon Chronicle, it is ubiquitous in the highly Latinate translation of Bede’s Ecclesiastical History.
Not surprisingly, Latin held the most pervasive influence on Old English in the area of vocabulary. Moreover, this sphere of influence provides the clearest index of the changing relationship between Old English and Latin speakers. In total approximately 450 Old English words, mostly nouns, were borrowed from Latin (Baugh, 106). Around 170 of these entered the Old English lexicon during the continental period (Hogg, 302; Williams, 57). These words pertain mostly to plants, household items, clothing and building materials. As such, they represent the influence of Vulgar (i.e. spoken) Latin rather than Classical (i.e. literate) Latin. It is uncertain how many words date from the second period of Latin influence. In general though, scholars maintain that there are slightly fewer borrowings dating from this period. With the exception of a comparatively larger number of words having to do with religion and learning, borrowings from this period pertain to the same subject matter as those of the first period (Hogg, 302-3). In strong contrast with the two preceding periods, the third period shows a marked increase in words concerning religion and learning. The influx of such words clearly reflects the influence of the literate, CL culture associated with the Church following the Christianization of the Anglo-Saxons. In addition to direct borrowings, Latin also influenced the Old English lexicon by occasioning the formation of semantic loans, loan translations (or calques) and loan creations. Consider, for example, the semantic loan Old English cniht for Latin discipulus, in which native Old English cniht, "boy" or "servant," assumes the additional sense of Latin discipulus, "disciple." Such translations are abundant in the Old English lexicon. Equally prevalent are loan translations, in which a Latin compound word is translated using morphologically equivalent native elements: e.g. Old English foreberan < Latin praeferre. Loan creations are also numerous. Like loan translations, loan creations translate the Latin word using native elements but with greater morphological freedom: e.g. Old English restedæg for Latin sabbatum.
The overall abundance of semantic loans, loan translations and loan creations suggests a final and more general truth concerning the influence of Latin on Old English. Despite the relatively extensive influence of Latin on Old English, Old English clearly shows a strong tendency to rely on native resources. That is to say, given the linguistic conditions of Old English period, one would expect Latin to have exerted a far greater influence than in fact our knowledge of Old English suggests.