This thesis investigates the semantic and syntactic factors that affect the encoding of the anaphoric direct object (ADO) in Brazilian Portuguese (BP). The ADO can be a full DP [+definite], an accusative clitic, a stressed pronoun, or a null element (whose nature is controversial in linguistic theory). This research aims to: (i) investigate how the semantic properties (animacy, specificity and conceptual genre) of the antecedent, its syntactic function and factors pertaining to the syntax/semantic interface (thematic role) affect the encoding of the ADO in different syntactic contexts (simple sentences and syntactic island) and/or discourse (answers to WH-questions and continuations of short narratives or informal conversations); (ii) verify the influence of schooling in the strategies of ADO encoding; and (iii) discuss the nature of the null forms produced. The theoretical background incorporates the conception of language conveyed in the Minimalist Program (CHOMSKY, 1995; 2005) and an approach to issues regarding the relative accessibility of the antecedent to be resumed (ARIEL, 2001; ARNOLD, 2010; BOCK; WARREN, 1985; SANDERS; GERNSBACHER, 2004) in the grammatical encoding of a sentence (LEVELT, 1989), in the light of an on-line model of grammatical computation (CORREA, 2006; 2008; CORREA; AUGUSTO, 2007) The working hypothesis is that the production of the ODA is a function of particular processing conditions and that the semantic and syntactic properties of the antecedent affect its relative accessibility, imposing restrictions on its resumption. Six elicited production experiments are reported. The syntactic context influenced the accessibility of the antecedents, predominantly recovered by full DPs, when between-sentences in the discourse; and by minimal forms (pronominals and null elements) in complex sentences. The effects of animacy and of specificity corroborate spontaneous production data, suggesting that the full pronoun is the default option for [+animated; +specific], while the null form is the default option for [-animated; +- specific] antecedents. The conceptual genre of the antecedent was not decisive for a particular form of encoding, but it seemed to enhance the specificity of the antecedent whose conceptual gender was known. The thematic role, by itself, does not determine the form of anaphoric resumption. However, the possibility of the null resumption of an fact/event previously mentioned makes it compatible with an alternative to the sentential clitic. Schooling increased the rates of accusative clitics, especially with [+animated] antecedents (as an alternative to tonic pronouns), showing the interference of the written language on the spoken language, as well as the productivity of this form for educated speakers. The syntactic function of the antecedent did not affect ADO production. The occurrence of the null element in island contexts corroborates the view that the null element is not a variable in BP. It is argued, in the light of the on-line model, that the accessibility of the antecedent determines the nature of null element: if the representation of the syntactic structure of the antecedent is still active in working memory, it can be retrieved as an ellipsis, to be restored at the semantic interface; if it is the phi features of the antecedent or the semantic representation of its referent that remain available, ADO is encoded as a pro.