The unaccusativity hypothesis (Burzio 1986; Levin & Rappaport Hovav 1995; Perlmutter 1978) posits that intransitive verbs may be divided into two broad classes: unaccusatives, whose sole argument is an internal argument and unergatives, whose sole argument is an external argument. In this dissertation I explore the idea that there is a similar, though less obvious, division among different types of transitive verbs using Spanish as the primary object language. The idea that transitivity is not a uniform phenomenon has been explored in many approaches to grammar (Cuervo 2003; Dixon & Aikenvald 2000; Hale & Keyser 1993, 2002; Hopper & Thompson 1980; Levin 1999; Marantz 1997, 2005). The main objective of this dissertation is to contribute in a meaningful way to the idea that there are different types of transitive verbs by (i) outlining a series of diagnostic tests in Spanish for separating certain types of transitive verbs into two broad classes that I label "class 1" and "class 2" and (ii) providing an analysis for why class 1 and class 2 transitive verbs have the properties that they do in this language. I limit the study principally to sets of verbs that have usually been characterized according to lexical semantic notions like "change of state" (such as "romper" = break; my "class 1") and "activity" (such as "leer" = read; my "class 2"). It is argued that the simplest generalization that captures the properties of these verbs is one that mirrors, to a large extent, the unaccusative-unergative distinction: class 1 verbs require an internal argument and may optionally omit their external argument whereas class 2 verbs require an external argument and may optionally omit their internal argument. I present a formal analysis of class 1 and class 2 verbs based on this generalization, claiming that it has positive consequences for understanding transitivity alternations, the interpretation and modification of participles and various uses of the reflexive ("se") clitic paradigm in Spanish. Finally, I propose that class 1 verbs form a continuum that includes unaccusative verbs while class 2 verbs form a continuum that includes unergative verbs. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]