In order to advance the scientific basis for message design, theories of belief, attitude, and intention change focusing on the importance of arguments must be joined with theories that deal more with a message’s executional (or format) features. Previous summaries of the literature on message effectiveness are reviewed. They provide the fact base needing explanation. They are therefore useful but fail to provide an explanatory mechanism for integrating message content and format elements. This paper takes steps in this direction arguing that processing and resource allocation theories (Lang, 2006; Stephenson & Southwell, 2006) can be integrated with theories of belief change (Petty & Cacioppo, 1986) to advance message effects theory and research. The mechanism employed generalizes from the mediational processes of the elaboration likelihood model, namely ability and motivation, arguing that message formatting features themselves affffect ability and motivation. Specifific predictions for the interaction of message format features and argument strength are derived through their impact on ability and motivation. Recent research reporting interaction between format features and argument strength is described in the context of the model’s predictions. Implications of the model for cumulating knowledge about message effffects and guiding future research are explored.