This dissertation examines the influence of lexical-semantic representations, conceptual similarity, and contextual fit on the processing of coordinated verb phrases. The study integrates information gleaned from current linguistic theory with current psycholinguistic approaches to examining the processing of coordinated verb phrases. It has been claimed that in coordinated phrases, one conjunct may influence the processing of a second conjunct if they are sufficiently similar. For example, The likelihood of adopting an intransitive analysis for the optionally transitive verb of a subordinated clause in sentences like Although the pirate ship sank the nearby British vessel did not send out lifeboats may be increased if the ambiguous verb (sank) is coordinated with a preceding, intransitively biased verb (halted and sank). Similarly, processing of the second conjunct may be facilitated when coordinated with a similar first conjunct. Such effects, and others in this vein have often been designated “parallelism effects.” However, notions of similarity underlying such effects have long been ill-defined. Many existing studies rely on relatively shallow features like syntactic category information or argument structure generalizations, such as transitive or intransitive, as a basis for structural comparison. But it may be that deeper levels of lexical-semantic representation and more varied, semantic or conceptual sources of information are also relevant to establishing similarity between conjuncts. In addition, little has been done to xi integrate parallelism effects to theories of the processing architecture underlying such effects, particularly for studies involving syntactic ambiguity resolution. Using two word-by-word reading and three eyetracking while reading experiments, I investigate what contribution detailed lexical-semantic representations, as well as conceptual and contextual information make towards establishing parallel coordination in the online processing of coordinated verb phrases. The five studies demonstrate that parallelism effects are indeed sensitive to deeper representational information, conceptual similarity, and contextual fit. Furthermore, by controlling for deeper representational information, it is demonstrated that expected facilitatory patterns arising from coordination of similar conjuncts may be disrupted. Implications for the architecture of the processing system are discussed, and it is argued that constraintbased/ competition models of processing best accommodate the pattern of results.