While there is a clear link between impairments of executive functions (EFs), i.e. cognitive control mechanisms that facilitate goal-directed behavior, and speech problems, it is so far unclear exactly which of the complex subdomains of EFs most strongly contribute to speech performance, as measured by verbal fluency (VF) tasks. Furthermore, the impact of intra-individual variability is largely unknown. This study on healthy participants (n = 235) shows that the use of a relevance vector machine approach allows for the prediction of VF performance from EF scores. Based on a comprehensive set of EF scores, results identified cognitive flexibility and inhibition as well as processing speed as strongest predictors for VF performance, but also highlighted a modulatory influence of fluctuating hormone levels. These findings demonstrate that speech production performance is strongly linked to specific EF subdomains, but they also suggest that inter-individual differences should be taken into account. Executive functions (EFs) refer to a set of cognitive processes that allow for goal-directed behavior through the regulation of various cognitive subprocesses. Since EFs permeate behavior, they also impact daily activities as well as social and personal development, including school or job success 1. The importance and pervasiveness of EFs has led different fields of study to investigate these control mechanisms with the goal of differentiating the various subdomains of EFs. This, in turn, has resulted in a number of different conceptualizations based on different approaches, all attempting to subdivide EFs into different domains. While a consensus does not yet exist about how exactly to subdivide and name EFs, there is general agreement that there are three core EFs: (1) cognitive flexibility, (2) working memory and (3) inhibition 1 (but see Karr et al. 2,3). Higher-order EFs, such as reasoning, planning and problem solving, are then built on the basis of these subdomains. The various sub-domains of EFs have been shown to be impaired in a number of neurological and psychiatric diseases, such as attention-deficit/hyperactivity disorder (ADHD) 4 , Parkinson's disease 5 , depression 6 and schizophrenia 7. Different diseases present their own typical EF deficits and clinical diagnosis attempts to assess the specific patterns of the disease. For example, in the case of Parkinson's disease, patients suffer from difficulties in dual-tasking which is reflected in the deficient combination of memorizing and manipulation of thoughts and tasks 8 but also in impaired speech characterized by semantic paraphasias and reduced word fluency due to a lack of EFs 5,9. To assess these symptoms different test batteries have been developed. These batteries, which include tests tapping into the different EF sub-domains, are used for neuropsychological assessment in both clinical settings and lab-based environments. Commonly used batteries are the Delis-Kaplan Executive Function System (D-KEFS) and the Vienna Test System, both of which offer a w...