The field of marketing strategy often makes the important assumption that marketing strategy should occur by first composing a plan on the basis of a careful review of environmental and firm information and then executing that plan. However, there are cases when the composition and execution of an action converge in time so that, in the limit, they occur simultaneously. The authors define such a convergence as improvisation and develop hypotheses to investigate the conditions in which improvisation is likely to occur and be effective. The authors test these hypotheses in a longitudinal study of new product development activities. Results show that organizational improvisation occurs moderately in organizations and that organizational memory level decreases and environmental turbulence level increases the incidence of improvisation. Results support traditional concerns that improvisation can reduce new product effectiveness but also indicate that environmental and organizational factors can reduce negative effects and sometimes create a positive effect for improvisation. These results suggest that, in some contexts, improvisation may be not only what organizations actually practice but also what they should practice to flourish.