The author's stated purpose is to answer the questions: (1) Do auxiliary verbs exist in Spanish? If so, what are the characteristics which distinguish them as a class, and what specific verbs are included in that class? (2) Is there, in particular, a class of modal auxiliaries? If so, what are their defining characteristics, and what is the membership of such a class? (3) If modals are found not to exist as such in deep structure, what analysis can be put forth to account for the special characteristics of those verbs which have traditionally been so classed? A brief review of traditional and current linguistic analyses is given and the author's analysis is presented in the form of a transformational generative grammar model. It is the author's view that there is "strong evidence" to suggest that modals are main verbs in deep structures. The traditional auxiliaries ("haber + do" and "estar + ndo"), however, are treated as auxiliaries rather than main verbs. Appended to this analysis are: Rules of the Base Component, Lexicon, Transformational Rules, and Exemplary Derivations. (JD)