Situations of sustained language contact between Spanish and English have existed in the United States since the early nineteenth century. Initial contact between these two languages in what is now the U.S. Southwest was the result of territorial expansion by English-speaking settlers. Later contact situations in New York and Florida were caused by economic and political circumstances facing Spanish speaking caribeños. As a result of this contact, English has exerted some degree of influence on the bilingual Spanish spoken in the United States. The structural results of contact range from subtle changes in articulation to broad changes in the lexicon, all of which have been studied to greater and lesser extents by linguists over the past century. This introduction provides a point of reference for these studies. The accumulation of structural influences from English, regardless of geographical location, is leading to a transformation in the linguistic structure of U.S. Spanish, thereby making it distinct from other varieties of this language.