The English and Spanish languages have been coexisting, influencing and confronting each other in Puerto Rico for over a Century. The authors address the central questions about this relationship between the two languages, beginning with an overview of the historical circumstances that brought the English language t o Puerto Rico, fr'om the colonial period to the associated free state (or Commonwealth) of the present. The authors seek to establish what is the true r öle of English to Puerto Ricans, both historically and currently, and how the language should be taught. The current political, social, economic and educational situations are reviewed in order to determine the function and problems of English on the Island. Second Language Acquisition research (SLA), Whole Language and Critical Thinking and Thing Skills language learning models are in turn considered äs they apply (or not) to the Puerto Rican context. They establish the dijferences between what is commonly considered bilingual education and the type of language education that tahesplace in Puerto Rico. The influence ofthe two languages upon each other is also discussed, especially äs it relates to the teaching-learning process. Language planning, a branch of the sociology of language, Supports a series of recommendations related to teaching English and researching the ESL learning process in Puerto Rico.