Two series of experiments were conducted in relation to the issues of how speakers select and plan linguistic representations during language production. The first was an aging and individual differences study relating performance on standard tests of executive functioning to performance on a blocked cyclic naming experiment. Few differences were found between the two age groups that could not be attributed to a decline in the speed of processing and shifting the focus of attention in the components of working memory. Combined group analyses revealed two separate processes influencing performance in the blocked cyclic naming task, with one being a proactive interference effect involving competition between items in the response set and the other being a distractor interference effect involving the intrusion of a previously presented item. The proactive interference effect was not modulated by semantic relatedness, except in the first cycle, and it was argued that this reflected competition between a set of activated lexical items, whereas the distractor interference effect was modulated by semantic relatedness, and it was argued that it was due to the persistence in the activation of a particular item after it was no longer relevant. The second series of sentence production experiments was intended to distinguish between different accounts of the scope of planning in sentence production by varying phrasal complexity and lexical variables thought to affect the ease of retrieving items at different levels of representation. Across the experiments, evidence was found, as in previous studies (e.g., Smith & Wheeldon, 1999) that the phrase is a scope of planning, as manipulations of initial phrase complexity consistently affected sentence onset latencies. However, only manipulations of the semantic properties of items interacted with phrasal complexity, whereas manipulations of lexical variables showed no such interactions. These results suggest that the phrasal scope is semantically-based (Allum & Wheeldon, 2007), and that planning involves greater processing of representations within the first phrase of the semantic level.